Answer:
The distance between the rocket and the satellite 10 seconds after the rocket started moving is of 934 feet.
Step-by-step explanation:
The distance between the rocket and the satellite, in feet, after t seconds, is given by the following equation:
[tex]P(t) = 9t^{2} + 34[/tex]
Find the distance between the rocket and the satellite 10 seconds after the rocket started moving.
This is P(10).
[tex]P(t) = 9t^{2} + 34[/tex]
[tex]P(10) = 9*(10)^{2} + 34 = 934[/tex]
The distance between the rocket and the satellite 10 seconds after the rocket started moving is of 934 feet.
The vector matrix[ 27 ]is dilated by a factor of 1.5 and then reflected across the X axis if the resulting matrix is a B then a equals an VE
Correct question:
The vector matrix [ [tex] \left[\begin{array}{ccc}2\\7\end{array}\right] [/tex] is dilated by a factor of 1.5 and then reflected across the x axis. If the resulting matrix is [a/b] then a=??? and b=???
Answer:
a = 3
b = 10.5
Step-by-step explanation:
Given:
Vector matrix = [tex] \left[\begin{array}{ccc}2\\7\end{array}\right] [/tex]
Dilation factor = 1.5
Since the vector matrix is dilated by 1.5, we have:
[tex] \left[\begin{array}{ccc}1.5 * 2\\1.5 * 7\end{array}\right] [/tex]
= [tex] \left[\begin{array}{ccc}3\\10.5\end{array}\right] [/tex]
Here, we are told the vector is reflected on the x axis.
Therefore,
a = 3
b = 10.5
Answer:
a = 3
b = -10.5
Step-by-step explanation:
got a 100% on PLATO
Please help I’m struggling:(
Jose's taxi charges $5 plus $0.30 per mile for fare in a city. Kathy's taxi charges $8
plus $0.20 per mile for fare in the city. At what distance would the charges for the
two taxis be the same?
Answer:
30 miles
Step-by-step explanation:
Jose's charges are ...
j = 5 + 0.30m . . . . . for m miles
Kathy's charges are ...
k = 8 +0.20m . . . . . for m miles
The charges are the same when ...
j = k
5 +0.30m = 8 + 0.20m
0.30m = 3 + 0.20m . . . . subtract 5
0.10m = 3 . . . . . . . . . . . . subtract 0.20m
m = 30 . . . . . . . . . . . . . . . multiply by 10
The charges will be the same for a distance of 30 miles.
The curvature of a plane parametric curve x = f(t), y = g(t) is $ \kappa = \dfrac{|\dot{x} \ddot{y} - \dot{y} \ddot{x}|}{[\dot{x}^2 + \dot{y}^2]^{3/2}}$ where the dots indicate derivatives with respect to t. Use the above formula to find the curvature. x = 6et cos(t), y = 6et sin(t)
Answer:
The curvature is modelled by [tex]\kappa = \frac{e^{-t}}{6\sqrt{2}}[/tex].
Step-by-step explanation:
The equation of the curvature is:
[tex]\kappa = \frac{|\dot {x}\cdot \ddot {y}-\dot{y}\cdot \ddot{x}|}{[\dot{x}^{2}+\dot{y}^{2}]^{\frac{3}{2} }}[/tex]
The parametric componentes of the curve are:
[tex]x = 6\cdot e^{t} \cdot \cos t[/tex] and [tex]y = 6\cdot e^{t}\cdot \sin t[/tex]
The first and second derivative associated to each component are determined by differentiation rules:
First derivative
[tex]\dot{x} = 6\cdot e^{t}\cdot \cos t - 6\cdot e^{t}\cdot \sin t[/tex] and [tex]\dot {y} = 6\cdot e^{t}\cdot \sin t + 6\cdot e^{t} \cdot \cos t[/tex]
[tex]\dot x = 6\cdot e^{t} \cdot (\cos t - \sin t)[/tex] and [tex]\dot {y} = 6\cdot e^{t}\cdot (\sin t + \cos t)[/tex]
Second derivative
[tex]\ddot{x} = 6\cdot e^{t}\cdot (\cos t-\sin t)+6\cdot e^{t} \cdot (-\sin t -\cos t)[/tex]
[tex]\ddot x = -12\cdot e^{t}\cdot \sin t[/tex]
[tex]\ddot {y} = 6\cdot e^{t}\cdot (\sin t + \cos t) + 6\cdot e^{t}\cdot (\cos t - \sin t)[/tex]
[tex]\ddot{y} = 12\cdot e^{t}\cdot \cos t[/tex]
Now, each term is replaced in the the curvature equation:
[tex]\kappa = \frac{|6\cdot e^{t}\cdot (\cos t - \sin t)\cdot 12\cdot e^{t}\cdot \cos t-6\cdot e^{t}\cdot (\sin t + \cos t)\cdot (-12\cdot e^{t}\cdot \sin t)|}{\left\{\left[6\cdot e^{t}\cdot (\cos t - \sin t)\right]^{2}+\right[6\cdot e^{t}\cdot (\sin t + \cos t)\left]^{2}\right\}^{\frac{3}{2}}} }[/tex]
And the resulting expression is simplified by algebraic and trigonometric means:
[tex]\kappa = \frac{72\cdot e^{2\cdot t}\cdot \cos^{2}t-72\cdot e^{2\cdot t}\cdot \sin t\cdot \cos t + 72\cdot e^{2\cdot t}\cdot \sin^{2}t+72\cdot e^{2\cdot t}\cdot \sin t \cdot \cos t}{[36\cdot e^{2\cdot t}\cdot (\cos^{2}t -2\cdot \cos t \cdot \sin t +\sin^{2}t)+36\cdot e^{2\cdot t}\cdot (\sin^{2}t+2\cdot \cos t \cdot \sin t +\cos^{2} t)]^{\frac{3}{2} }}[/tex]
[tex]\kappa = \frac{72\cdot e^{2\cdot t}}{[72\cdot e^{2\cdot t}]^{\frac{3}{2} } }[/tex]
[tex]\kappa = [72\cdot e^{2\cdot t}]^{-\frac{1}{2} }[/tex]
[tex]\kappa = 72^{-\frac{1}{2} }\cdot e^{-t}[/tex]
[tex]\kappa = \frac{e^{-t}}{6\sqrt{2}}[/tex]
The curvature is modelled by [tex]\kappa = \frac{e^{-t}}{6\sqrt{2}}[/tex].
In the parallelogram below, solve for x and y. (Give your answer as a decimal, when necessary)
Answer: x = 15, y = 12.5
Step-by-step explanation:
The sum of the three angle measures of a triangle equals 180ᴼ
Since these triangles are vertical, the measures are congruent.
45 + 60 = 105
180 - 105 = 75
So now we know that 5x = 75ᴼ and 6y = 75ᴼ.
To find x, divide 75 by 5
75 / 5 = 15
x = 15
To find y, divide 75 by 6
75 / 6 = 12.5
y = 12.5
A ship traveled at an average rate of 25 miles per hour going west. It then traveled at an average rate of 19 miles per hour heading north. If the ship traveled a total of 145 miles in 7 hours, how many miles were traveled heading west?
Answer: 19.5 miles or 108.75 miles
Step-by-step explanation:
Let ship traveled to the west x hours and then to the north y hours. Total 7 hours. So we can write 1st equation
x+y=7 (1)
The ship traveled to the west x hours with speed 25 miles/h - the distance 25*x
The ship traveled to the north y hours with speed 19 miles/hour - the distance 19*y
Note that the angle between north and west directions is 90 degrees.
So if the initial traveling point is A, the final travelling point ic C and the point , where ther the ship has changed the travelling direction from West to North is B.
So we have the right triangle ABC, where B angle is right=90 degrees.
AB side=25*x, BC side= 19*y and AC side 145 miles.
According to Pithagor theorem we can write
AC^2=AB^2+BC^2
21025=625*x^2+ 361*y^2 (2)
Solve the system of equations (1) and (2)
y=7-x
625*x^2+361*(7-x)^2=21025
625*x^2+361*(49-14x+x^2)=21025
625*x^2+17689-5054*x+361*x^2=21025
986*x^2- 5054*x-3336=0 dividing on 2 we'll get
493*x^2-2527*x-1668=0
D=3096433 sqrt(D)=appr 1760
x1=(2527-1760)/493/2= appr 0.78 h
x2=(2527+1760)/493/2=appr 4.35 h
So the problem has 2 solutions :
heading west the ship traveled or 0.78*25= 19.5 miles
Or 4.35*25= 108.75 miles
Answer:
let w = time heading west at 25 mph
the total time is 7 hrs, therefore
(7-w) = time heading north at 19 mph
Distance = speed * time
25w + 19(7-w) = 145
25w + 133 - 19w = 145
25w - 19w = 145 - 133
6w = 12
w = 12/6
w = 2 hrs traveling west
therefore
2 * 25 = mile going west
Confirm this solution, 7 - 2 = 5 hrs going north
19 * 5 = 95mi
25 * 2 = 50mi
--------------
total dist 145 mi
The Ball Corporation's beverage can manufacturing plant in Fort Atkinson, Wisconsin, uses a metal supplier that provides metal with a known thickness standard deviation σ = .000586 mm. Assume a random sample of 59 sheets of metal resulted in an x¯ = .2905 mm. Calculate the 95 percent confidence interval for the true mean metal thickness.
Answer:
The 95 percent confidence interval for the true mean metal thickness is between 0.2903 mm and 0.2907 mm
Step-by-step explanation:
We have that to find our [tex]\alpha[/tex] level, that is the subtraction of 1 by the confidence interval divided by 2. So:
[tex]\alpha = \frac{1-0.95}{2} = 0.025[/tex]
Now, we have to find z in the Ztable as such z has a pvalue of [tex]1-\alpha[/tex].
So it is z with a pvalue of [tex]1-0.025 = 0.975[/tex], so [tex]z = 1.96[/tex]
Now, find the margin of error M as such
[tex]M = z*\frac{\sigma}{\sqrt{n}}[/tex]
In which [tex]\sigma[/tex] is the standard deviation of the population and n is the size of the sample.
[tex]M = 1.96\frac{0.000586}{\sqrt{59}} = 0.0002[/tex]
The lower end of the interval is the sample mean subtracted by M. So it is 0.2905 - 0.0002 = 0.2903 mm
The upper end of the interval is the sample mean added to M. So it is 0.2905 + 0.0002 = 0.2907 mm
The 95 percent confidence interval for the true mean metal thickness is between 0.2903 mm and 0.2907 mm
to prove triangleABC is isosceles, which of the following statements can be used in the proof?
&
given circleR, how is it known that QS = YT?
(idk the answers i guessed)
Answer:
Step-by-step explanation:
In an isosceles triangle, the base angles are equal. This also means that the length of two sides of the triangle are equal. Looking at triangle ABC, to prove that it is an isosceles triangle, then
Angle CAB = angle CBA
For the second question, to determine how it is known that QS is equivalent to YT, we would recall that the diameter of a circle passes through the center and from one side of the circle to the other side. Assuming R is the center of the circle, then QS and YT are the diameters of the circle and also the diagonals of the rectangle. Thus, the correct option is
The diameters act as diagonals
Find the amount in an account where $500 is invested at 2.5% compounded continuously for period of 10 years
Hi
500 *1.025^10 ≈ 640.04
Match each correlation coefficient, r, to its description.
r = −0.08
r = −0.83
r = 0.96
r = 0.06
1.) strong negative correlation
2.) weak positive correlation
3.) weak negative correlation
4.) strong positive correlation
The answers are in order
r = −0.08 --> weak negative correlation
r = −0.83 --> strong negative correlation
r = 0.96 --> strong positive correlation
r = 0.06 --> weak positive correlation
The match of each correlation is given by,
r = −0.08 implies a weak negative correlation
r = −0.83 implies a strong negative correlation
r = 0.96 implies strong positive correlation
r = 0.06 implies weak positive correlation.
We have given that,
The correlation coefficient, r, to its description.
A B
r = −0.08 strong negative correlation
r = −0.83 weak positive correlation
r = 0.96 weak negative correlation
r = 0.06 strong positive correlation
We have to match the given relation
What is the positive and negative correlation?If the correlation coefficient is greater than zero, it is a positive relationship. Conversely, if the value is less than zero, it is a negative relationship.
So the correct match is,
r = −0.08 implies a weak negative correlation
r = −0.83 implies strong negative correlation
r = 0.96 implies strong positive correlation.
r = 0.06 is implies weak positive correlation.
To learn more about the correlation visit:
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Equations and Functions
Answer:
Subtract the 2w to both sides of the equal sign.
Step-by-step explanation:
Since we want the equation to be in terms of l, we need to isolate the term first. To do so, we will need to subtract 2w on both sides to start out.
Perform the indicated operation.
Answer:
√75 = 5√3 and √12 = 2√3 so √75 + √12 = 5√3 + 2√3 = 7√3.
Answer:
[tex] 7\sqrt{3} [/tex]
Step-by-step explanation:
[tex] \sqrt{12} \: can \: be \: simplified \: as \: 2 \sqrt{3} \: and \: \sqrt{75} \: canbe \: simplified \: as \: 5 \sqrt{3} \\ after \: simplifying \: we \: can \: add \: them \: up \\ 2 \sqrt{3} + 5 \sqrt{3} = 7 \sqrt{3} [/tex]
An object is launched directly in the air speed of 16 feet per second from a platform located 5 feet above the ground. The position of the object can be modeled using the function f(x)=-16t^2+16t+5, where t is the time of seconds and f(t) is the height of the object. What is the maximum height in feet that the object will reach?
Answer:
The maximum height that the object will reach is of 9 feet.
Step-by-step explanation:
Vertex of a quadratic function:
Suppose we have a quadratic function in the following format:
[tex]f(x) = ax^{2} + bx + c[/tex]
It's vertex is the point [tex](x_{v}, f(x_{v})[/tex]
In which
[tex]x_{v} = -\frac{b}{2a}[/tex]
If a<0, the vertex is a maximum point, that is, the maximum value happens at [tex]x_{v}[/tex], and it's value is [tex]f(x_{v})[/tex]
In this question:
[tex]f(t) = -16t^{2} + 16t + 5[/tex]
So
[tex]a = -16, b = 16[/tex]
The instant of the maximum height is:
[tex]t_{v} = -\frac{16}{2*(-16)} = 0.5[/tex]
The maximum height is:
[tex]f(0.5) = -16*(0.5)^2 + 16*0.5 + 5 = 9[/tex]
The maximum height that the object will reach is of 9 feet.
Answer:
24
Step-by-step explanation:
A bus can carry a maximum of 60 passengers. Each row accommodates the same number of passengers. If two rows are added then each row would accommodate one passenger less for the bus to carry maximum number of passengers. Determine number of rows in the bus and no. Of passengers per row
Answer:
10 rows with 6 passengers per row
Step-by-step explanation:
Let x be the number of rows and y the number of passengers per row.
Then we can interpret the story as the following two equations:
xy=60
(x+2)(y-1)=60
Solving these two equations:
y=60/x
(x+2)(60/x-1)=60 (substitute y)
60 - x + 120/x - 2 = 60 (multiply by -x)
x² + 2x - 120 = 0 (factor)
(x-10)(x+12) = 0
x = 10
y = 60/10 = 6
and indeed 10 * 6 = 60 and also 12 * 5 = 60
A company determined that the marginal cost, Upper C prime (x )of producing the xth unit of a product is given by Upper C prime (x )equalsx Superscript 4minus2x. Find the total cost function C, assuming that C(x) is in dollars and that fixed costs are $6000.
Answer:
C(x) = 0.2x^5 - x^2 + 6000
Step-by-step explanation:
Given in the question are restated as follows:
Marginal cos = C'(x) = x^4 - 2x ...................... (1)
Note that marginal cost (C'(x)) refers to the change in the total cost (C(x)) as a result of one more unit increase in the quantity produced. That is, MC refers to the additional cost incurred in order to produce one more unit of a good.
Therefore, TC can be obtained by integrating equation (1) as follows:
C(x) = ∫C'(x) = ∫[x^4 - 2x]dx
C(x) = 1/5x^5 - 2/2x^2 + F ................................ (2)
Where F is the fixed cost. Since the fixed cost is given as $6,000 in the question, we substitute it for F into equation (2) and solve as follows:
C(x) = 0.2x^5 - x^2 + 6000 ......................... (3)
Equation (3) is the total cost function C.
Please answer this correctly
The correct answer is 5.5988 x [tex]10^{-3}[/tex] = 0.0055988
Explanation:
In mathematics and related areas, it is common the expression [tex]10^{n}[/tex] (n = a whole number) that multiplies a number, this is known as scientific notation, and it used to express long numbers concisely. This type of notation implies the exponent number or n represents the number of zeros in the number or the number of spaces after/before the decimal period.
Additionally, if the exponent is positive this means the zeros are placed to the right of the number, while a negative exponent shows the zeros are on the left. For example 7 x [tex]10^{3}[/tex] is equal to 7000 because the exponent indicates there are three zeros to the right of 7 or you need to move three spaces the period to the right, which is located right after 7. According to this, the expression 5.5988 x [tex]10^{-3}[/tex] indicates there are 3 zeros to the left of this number or that you need to move three spaces the period and add zeros in these spaces, which is equal to 0.0055988. Therefore, both numbers are equal (=)
what is the gfc of 16 and 8
Answer:
Greatest common factor of 16 and 8 is 8 .....Simplify: 1. (x−1)+(12−7.5x) 2. b−(4−2b)+(3b−1) 3. (2p+1.9)−(7−p)
Answer:
1. -6.5x+11
2. 6b-5
3. 3p-5.1
Step-by-step explanation:
[tex]1. \\(x-1)+(12-7.5x)=\\x-1+12-7.5x=\\x-7.5x-1+12=\\-6.5x-1+12=\\-6.5x+11\\\\2.\\b-(4-2b)+(3b-1)=\\b-4+2b+3b-1=\\b+2b+3b-4-1=\\3b+3b-4-1=\\6b-4-1=\\6b-5\\\\3.\\(2p+1.9)-(7-p)=\\2p+1.9-7+p=\\2p+p+1.9-7=\\3p+1.9-7=\\3p-5.1[/tex]
What the answer fast
Answer:
∠CDE
Step-by-step explanation:
Name it by the order of the letters with the point of the angle in the middle
Please help!!! I'm really confused.
The value of root 10 is between 3 and 3.5
I NEED HELP PLEASE, THANKS! :)
Answer: G ∩ M = {Anael, Max}
G U S = {Acel, Acton, Anael, Barek, Carl, Carlin, Dario, Kai, Max}
Step-by-step explanation:
intersection ∩ - items found in BOTH sets
union U - the joining of the sets. include EVERYTHING in the sets.
G = (Acel, Acton, Anael, Carl, Dario, Max}
S = {Anael, Barek, Bay, Carlin, Kai, Max}
G ∩ S: Anael and Max are found in both sets
G = (Acel, Acton, Anael, Carl, Dario, Max}
S = {Acton, Anael, Barek, Carlin, Dario, Kai}
G U S: include everything in G and everything in S. If found in both sets, only list it once.
G U S = {Acel, Acton, Anael, Barek, Carl, Carlin, Dario, Kai, Max}
Notice that Acton and Anael are in both sets but we only list them once.
Simplify: 1. 4x−(1−2x)+(2x−7) 2. (3−0.4a)−(10−0.8a)
Answer:1.8(x -1)
2.0.4a -7
Step-by-step explanation:
Which expression represents the phrase 4 times the sum of 9 and 6
A. 4x (9+6)
B.4x 9+6
C.9+ 6x4
D. 9+ (6x4)
Answer:
The answer is option A
4 x ( 9 + 6)
Hope this helps you
A person who yells at an official who made a bad call is just displaying a competitive spirit. Please select the best answer from the choices provided. T F
Answer:
the answer is false
Step-by-step explanation:
FALSE. A person who yells at an official is not showing a competitive spirit.
What is a Competitive Spirit?A competitive spirit shows the following attributes:
Communicates respectShows sportsmanshipValues process among others.A person yelling at an official is not a way of communicating respect. Therefore, it is FALSE to say it is a display of competitive spirit.
Learn more about competitive spirit on:
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#SPJ2
PLEASE ANSWER FAST, THANKS! :)
Answer:
Step-by-step explanation:
k = 3 ; 2k + 2 = 2*3 + 2 = 6 + 2 = 8
k = 4; 2k + 2 = 2*4 + 2 = 8 +2 = 10
k =5; 2k + 2 = 2*5 +2 = 10+2 = 12
k=6; 2k +2 = 2*6 + 2 = 12+2 = 14
k = 7 ; 2k + 2 = 2*7 +2 = 14 +2 = 16
k = 8 ; 2k + 2 = 2*8 + 2 = 16 +2 = 18
∑ (2k + 2) = 8 + 10 + 12 + 14 + 16 + 18 = 78
Express $0.\overline{1}+0.\overline{01}+0.\overline{0001}$ as a common fraction.
Answer:
[tex]\dfrac{1213}{9999}[/tex]
Step-by-step explanation:
We are required to express [tex]0.\overline{1}+0.\overline{01}+0.\overline{0001}[/tex] as a common fraction.
The bar on top of the decimal part indicates the decimal number is a repeating decimal.
Therefore:
[tex]0.\overline{1}=\dfrac{1}{10-1}= \dfrac{1}{9}\\\\0.\overline{01}=\dfrac{1}{100-1}= \dfrac{1}{99}\\\\0.\overline{0001}=\dfrac{1}{10000-1}= \dfrac{1}{9999}\\\\\\$Therefore$:\\0.\overline{1}+0.\overline{01}+0.\overline{0001} \\=\dfrac{1}{9}+\dfrac{1}{99}+\dfrac{1}{9999}\\\\=\dfrac{1213}{9999}[/tex]
Find the perimeter and total area of the composite shape shown below. All measurements are given in inches. Use pi = 3.14 in any formulas used.
Answer:
Step-by-step explanation:
The composite shape consists of a semi circle and a triangle. The formula for determining the perimeter of a semicircle is expressed as
Perimeter = 1/2 × 2πr = πr
Since radius, r = 3, then
Perimeter of semi circle = 3 × 3.14 = 9.42 inches
Perimeter of composite shape = 9.42 + 5 + 5 = 19.42 inches
Area of semi circle = 1/2 × πr²
Area of semicircle = 1/2 × 3.14 × 3² = 14.13 inches²
Area of triangle = 1/2 × base × height
Area of triangle = 1/2 × 6 × 4 = 12 inches²
Area of composite shape = 14.13 + 12 = 26.13 inches²
The perimeter and area of the composite shape is:
B. Perimeter = 19.42 inches; Area = 26.13 square inchesRecall:
Area of a circle = πr²
Perimeter of circle = 2πr
Area of triangle = 1/2(bh)
The composite shape given is composed of a triangle and a semicircle.
Perimeter of the composite shape = Perimeter of semicircle + the length of the two sides of the triangle
Perimeter = 1/2(2 × 3.14 × 3) + 2(5) = 19.42 inches
Area of the composite shape = area of semicircle + area of triangle
Area = 1/2(3.14 × 3²) + 1/2(6 × 4)
Are = 14.13 + 12
Area of the composite shape = 26.13 square inches.
Therefore, the perimeter and area of the composite shape is:
B. Perimeter = 19.42 inches; Area = 26.13 square inchesLearn more about area and perimeter of composite shapes on:
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An observer for a radar station is located at the origin of a coordinate system. Find the bearing of an airplane located at the point (0,negative 4). Express the bearing using both methods.
Answer:
Step-by-step explanation:
I can help
HELP PLEASE ITS FOR PLATO
Answer:
i think it might be A. 0.2
Step-by-step explanation:
Rewrite the following statement in the form ∀x ______, if _______ then _______ (where each of the second two blanks are sentences involving the variable x) Every valid argument with true premises has a true conclusion.
Answer:
"Vx: if x is a valid argument with true premises then x has a true conclusion"
In a symbol form
Vx ( P(x) ⇒ 2(x) )
Step-by-step explanation:
The Following statement in the form ∀x ______, if _______ then _______ is a valid argument and this because any valid argument with "true premises" has a "true conclusion" as well
we will rewrite this statement in a universal condition statement form
assume x is a valid argument with true premises
then the following holds true
p(x) : x is a valid argument with true premises
q(x) : x has true conclusion
applying universal conditional statement
"Vx, if x is a valid argument with true premises then x has a true conclusion"
In a symbol form
Vx ( P(x) ⇒ 2(x) )
Suppose that E(θˆ1) = E(θˆ2) = θ, V(θˆ 1) = σ2 1 , and V(θˆ2) = σ2 2 . Consider the estimator θˆ 3 = aθˆ 1 + (1 − a)θˆ 2. a Show that θˆ 3 is an unbiased estimator for θ. b If θˆ1 and θˆ2 are independent, how should the constant a be chosen in order to minimize the variance of θˆ3?
Answer:
Step-by-step explanation:
Given that:
[tex]E( \hat \theta _1) = \theta \ \ \ \ E( \hat \theta _2) = \theta \ \ \ \ V( \hat \theta _1) = \sigma_1^2 \ \ \ \ V(\hat \theta_2) = \sigma_2^2[/tex]
If we are to consider the estimator [tex]\hat \theta _3 = a \hat \theta_1 + (1-a) \hat \theta_2[/tex]
a. Then, for [tex]\hat \theta_3[/tex] to be an unbiased estimator ; Then:
[tex]E ( \hat \theta_3) = E ( a \hat \theta_1+ (1-a) \hat \theta_2)[/tex]
[tex]E ( \hat \theta_3) = aE ( \theta_1) + (1-a) E ( \hat \theta_2)[/tex]
[tex]E ( \hat \theta_3) = a \theta + (1-a) \theta = \theta[/tex]
b) If [tex]\hat \theta _1 \ \ and \ \ \hat \theta_2[/tex] are independent
[tex]V(\hat \theta _3) = V (a \hat \theta_1+ (1-a) \hat \theta_2)[/tex]
[tex]V(\hat \theta _3) = a ^2 V ( \hat \theta_1) + (1-a)^2 V ( \hat \theta_2)[/tex]
Thus; in order to minimize the variance of [tex]\hat \theta_3[/tex] ; then constant a can be determined as :
[tex]V( \hat \theta_3) = a^2 \sigma_1^2 + (1-a)^2 \sigma^2_2[/tex]
Using differentiation:
[tex]\dfrac{d}{da}(V \ \hat \theta_3) = 0 \implies 2a \ \sigma_1^2 + 2(1-a)(-1) \sigma_2^2 = 0[/tex]
⇒
[tex]a (\sigma_1^2 + \sigma_2^2) = \sigma^2_2[/tex]
[tex]\hat a = \dfrac{\sigma^2_2}{\sigma^2_1+\sigma^2_2}[/tex]
This implies that
[tex]\dfrac{d}{da}(V \ \hat \theta_3)|_{a = \hat a} = 2 \ \sigma_1^2 + 2 \ \sigma_2^2 > 0[/tex]
So, [tex]V( \hat \theta_3)[/tex] is minimum when [tex]\hat a = \dfrac{\sigma_2^2}{\sigma_1^2+\sigma_2^2}[/tex]
As such; [tex]a = \dfrac{1}{2}[/tex] if [tex]\sigma_1^2 \ \ = \ \ \sigma_2^2[/tex]