Exam 14: Functions of Several Variables

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Find the sum of the squared errors for the linear model f(x)f ( x ) and the quadratic model g(x)g ( x ) using the given points. f(x)=1.6x+6,g(x)=0.29+2.2x+6 (-3,2),(-2,2),(-1,4),(0,6),(18)

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Find the four second partial derivatives. Observe that the second mixed partials are equal. z=x2+8xy+6y2z = x ^ { 2 } + 8 x y + 6 y ^ { 2 }

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Use Lagrange multipliers to minimize the function f(x,y,z)=x2+y2+z2f ( x , y , z ) = x ^ { 2 } + y ^ { 2 } + z ^ { 2 } subject to the following constraint. x+y+z21=0x + y + z - 21 = 0 Assume that x, y, and z are positive.

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Evaluate the double integral 010y(3x+2y)dxdy\int _ { 0 } ^ { 1 } \int _ { 0 } ^ { y } ( 3 x + 2 y ) d x d y . Round your answer to two decimal places, where applicable.

(Multiple Choice)
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Examine the function f(x,y)=x312xy+y3+4f ( x , y ) = x ^ { 3 } - 12 x y + y ^ { 3 } + 4 for relative extrema and saddle points.

(Multiple Choice)
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A company sells two products whose demand functions are given by x1 = 500 - 3p1 and x2 = 750 - 2.4p2 . So, the total revenue is given by R = x1p1 + x2p2 . Estimate the average revenue if the price p1 varies between $35 and $60 and the price p2 varies between $35 and $60.

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A rectangular box is resting on the xyx y -plane with one vertex at the origin. The opposite lies in the plane Find the dimensions that maximize the volume. (Hint: Maximize V=xyzV = x y z subject to the constraint 2x+3y+5z90=02 x + 3 y + 5 z - 90 = 0 ).

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A company manufactures two types of wood-burning stoves: a freestanding model and a fireplace-insert model. The cost function for producing x freestanding and y fireplace-insert stoves is C=30xy+160x+195y+1050C = 30 \sqrt { x y } + 160 x + 195 y + 1050 . Find the marginal costs ( C/x\partial C / \partial x and c/y\partial c / \partial y ) when x=60x = 60 and y=10y = 10 . Round your answers to two decimal places.

(Multiple Choice)
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The value A(t,r)A ( t , r ) of an investment of $4,000 after t years in an account for which the interest rate 100r% is compounded continuously is given by the function A(t,r)=4,000ertA ( t , r ) = 4,000 e ^ { r t } dollars. Write the partial derivative At\frac { \partial A } { \partial t }

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Determine whether the statement is true or false. If it is false, explain why or give an example that shows it is false. Data that are modeled by y=3.29x4.17y = 3.29 x - 4.17 have a negative correlation.

(Multiple Choice)
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Examine the function given below for relative extrema and saddle points. f(x,y)=f ( x , y ) = (x1)2+(y3)2( x - 1 ) ^ { 2 } + ( y - 3 ) ^ { 2 }

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The two planes x8y9z=4x - 8 y - 9 z = 4 and 4x21y7z=44 x - 21 y - 7 z = - 4 are parallel.

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