Exam 13: Introduction to Functions of Several Variables

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 For f(x,y)=eysin3x, evaluate fx at the point (π,0)\text { For } f ( x , y ) = e ^ { y } \sin 3 x \text {, evaluate } f _ { x } \text { at the point } ( \pi , 0 ) \text {. }

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 For f(x,y)=sin(9xy), evaluate fy at the point (2,π4)\text { For } f ( x , y ) = \sin ( 9 x y ) \text {, evaluate } f _ { y } \text { at the point } \left( 2 , \frac { \pi } { 4 } \right)

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Differentiate implicitly to find wx, given x2+y2+z27yw+2w2=4\frac { \partial w } { \partial x } \text {, given } x ^ { 2 } + y ^ { 2 } + z ^ { 2 } - 7 y w + 2 w ^ { 2 } = 4

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The material for constructing the base of an open box costs 1.5 times as much per unit area as the material for constructing the sides. For a fixed amount of money $150.00, find theDimensions of the box of largest volume that can be made.

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Find the critical points of the function f(x,y,z)=(x+7)2+(7y)2+(z+6)2f ( x , y , z ) = ( x + 7 ) ^ { 2 } + ( 7 - y ) ^ { 2 } + ( z + 6 ) ^ { 2 } and from the form of the function, determine whether a relative maximum or a relative minimum occurs at each point.

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Suppose the utility function U=f(x,y) is a measure of the utility (or satisfaction) U = f ( x , y ) \text { is a measure of the utility (or satisfaction) } derived by a person from the consumption of two products x and y. Determine the marginal utility of product if the utility function is U=3x2+xy8y2U = - 3 x ^ { 2 } + x y - 8 y ^ { 2 }

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Find the directional derivative of the function at P in the direction of v\overrightarrow { \mathbf { v } } \text {. } f(x,y)=x5y5,P(5,4),v=22(i^+j^)f ( x , y ) = x ^ { 5 } - y ^ { 5 } , P ( 5,4 ) , \quad \overrightarrow { \mathbf { v } } = \frac { \sqrt { 2 } } { 2 } ( \hat { \mathbf { i } } + \hat { \mathbf { j } } )

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Find and simplify the function f(x,y)=72x25y2 at the given value (3,3)f ( x , y ) = 7 - 2 x ^ { 2 } - 5 y ^ { 2 } \text { at the given value } ( 3,3 )

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Find the total differential for the function w=4z3ysinxw = 4 z ^ { 3 } y \sin x

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 Let w=xycosz, where x=t3,y=t5, and z=arccost. Find dwdt\text { Let } w = x y \cos z \text {, where } x = t ^ { 3 } , y = t ^ { 5 } \text {, and } z = \arccos t \text {. Find } \frac { d w } { d t } \text {. }

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Find the partial derivative zy for the function z=cos(x5+y5)\frac { \partial z } { \partial y } \text { for the function } z = \cos \left( x ^ { 5 } + y ^ { 5 } \right)

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Suppose the formula for wind chill C (in degrees Fahrenheit) is given by C=35.71+0.6217T35.72v0.16+0.4272Tv0.16C = 35.71 + 0.6217 T - 35.72 v ^ { 0.16 } + 0.4272 T v ^ { 0.16 } where vv is the wind speed in miles per hour and TT is the temperature in degrees Fahrenheit. The wind speed is 23±323 \pm 3 miles per hour and the temperature is 8±18 ^ { \circ } \pm 1 ^ { \circ } Fahrenheit. Use dCd C to estimate the maximum possible propagated error in calculating the wind chill. Round your answer to four decimal places.

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 For f(x,y)=x2xy+y25x+y find all values of x and y such that fx(x,y)=0\text { For } f ( x , y ) = x ^ { 2 } - x y + y ^ { 2 } - 5 x + y \text { find all values of } x \text { and } y \text { such that } f _ { x } ( x , y ) = 0 and fy(x,y)=0f _ { y } ( x , y ) = 0 simultaneously.

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Find three positive numbers x, y, and z whose sum is 30 and the sum of the squares is a minimum.

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 Find ws using the appropriate Chain Rule for w=y38x2y where x=es and \text { Find } \frac { \partial w } { \partial s } \text { using the appropriate Chain Rule for } w = y ^ { 3 } - 8 x ^ { 2 } y \text { where } x = e ^ { s } \text { and } y=ety = e ^ { t } , and evaluate the partial derivative at s=2s = - 2 and t=3t = 3 . Round your answer to two decimal places.

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 Given f(x,y)=xcosy, use the total differential to approximate Δz at (2,4)\text { Given } f ( x , y ) = x \cos y \text {, use the total differential to approximate } \Delta z \text { at } ( 2,4 ) towards (2.4,1.05)( 2.4,1.05 ) . Round your answer to four decimal places.

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The radius of a right circular cylinder is increasing at a rate of 6 inches per minute, and the height is decreasing at a rate of 4 inches per minute. What is the rate of change of the volumeWhen the radius is 14 inches and the height is 32 inches?

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Suppose the period T of a pendulum of length L is T=2πLg where g is the T = 2 \pi \sqrt { \frac { L } { g } } \text { where } g \text { is the } acceleration due to gravity. A pendulum is moved from the Canal Zone, where g=32.01 feet per g = 32.01 \text { feet per } second per second, to Greenland, where g=32.83g = 32.83 feet per second per second. Because of the change in temperature, the length of the pendulum changes from 2.6 feet to 2.45 feet. Approximate the Change in the period of the pendulum. Round your answer to four decimal places.

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Find the limit limΔy0f(x,y+Δy)f(x,y)Δy for the function f(x,y)=7x+5xy2y\lim _ { \Delta y \rightarrow 0 } \frac { f ( x , y + \Delta y ) - f ( x , y ) } { \Delta y } \text { for the function } f ( x , y ) = 7 x + 5 x y - 2 y

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 Find lim(x,y)(a,b)[f(x,y)g(x,y)) by using the limits lim(x,y)(a,b)f(x,y)=7 and \text { Find } \lim _ { ( x , y ) \rightarrow ( a , b ) } [ f ( x , y ) - g ( x , y ) ) \text { by using the limits } \lim _ { ( x , y ) \rightarrow ( a , b ) } f ( x , y ) = 7 \text { and } lim(x,y)(a,b)g(x,y)=4\lim _ { ( x , y ) \rightarrow ( a , b ) } g ( x , y ) = 4

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