Exam 14: Functions of Several Variables

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Use a double integral to find the area of the region bounded by the graphs of y=x13/2y = x ^ { 13 / 2 } and y=xy = x .

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Evaluate fxf _ { x } and fyf _ { y } for the function f(x,y)=7x3+xyy3f ( x , y ) = 7 x ^ { 3 } + x y - y ^ { 3 } at the point (4,6)( 4 , - 6 ) .

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Test for relative extrema and saddle points. z=x28xy+y2+120xz = x ^ { 2 } - 8 x y + y ^ { 2 } + 120 x

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Examine the function f(x,y)=5x28y23x+8y+4f ( x , y ) = 5 x ^ { 2 } - 8 y ^ { 2 } - 3 x + 8 y + 4 for relative extrema.

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An agronomist used four test plots to determine the relationship between the wheat yield yy (in bushels per acre) and the amount of fertilizer xx (in pounds per acre). The results are shown in the table. Fertilizer, x 100 150 200 250 Yield, y 35 44 50 56 (a) Use the regression capabilities of a graphing utility or a spreadsheet to find the least squares regression line for the data. (b) Estimate the yield for a fertilizer application of 160 pounds per acre.

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Find the critical points of the function f(x,y,z)=(x4)2+(7y)2+(z2)2f ( x , y , z ) = ( x - 4 ) ^ { 2 } + ( 7 - y ) ^ { 2 } + ( z - 2 ) ^ { 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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Evaluate the function at the given values of the independent variables. z=x3+2xy+3y2,x=9,y=7z = x ^ { 3 } + 2 x y + 3 y ^ { 2 } , \quad x = - 9 , y = 7

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Evaluate the double integral 0403(3x+4y)dydx\int _ { 0 } ^ { 4 } \int _ { 0 } ^ { 3 } ( 3 x + 4 y ) d y d x .

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Describe the domain and range of the function. f(x,y)=49x2y2f ( x , y ) = \sqrt { 49 - x ^ { 2 } - y ^ { 2 } }

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Sketch the region RR whose area is given by the following double integral. 04x2dydx\int _ { 0 } ^ { 4 } \int _ { \sqrt { x } } ^ { 2 } d y d x

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Describe the trace of the surface given by the function below y2+z2x2=1y ^ { 2 } + z ^ { 2 } - x ^ { 2 } = 1 in the xz-plane.

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Evaluate the double integral 00xye(4x2+9y2)dxdy\int _ { 0 } ^ { \infty } \int _ { 0 } ^ { \infty } x y e ^ { - \left( 4 x ^ { 2 } + 9 y ^ { 2 } \right) } d x d y .

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Set up an integral for both orders of integration, and use the more convenient order to evaluate the integral below over the region R. Ryx2+y2dA\iint _ { R } \frac { y } { x ^ { 2 } + y ^ { 2 } } d A RR : trianglebounded by y=5x,y=6xy = 5 x , y = 6 x , and x=5x = 5

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The sum of the length (denote by z) and the girth (perimeter of a cross section) of packages carried by a delivery service cannot exceed 60 inches. Find the dimensions of the rectangular package of largest volume that may be sent.

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A microbiologist must prepare a culture medium in which to grow a certain type of bacteria. The percent of salt contained in this medium is given by S=12xyzS = 12 x y z where x,y,x , y, and zz are the nutrient solutions to be mixed in the medium. For the bacteria to grow, the medium must be 13% salt. Nutrient solutions x,y,x , y, and zz cost $1, $2, and $3 per liter, respectively. How much of each nutrient solution should be used to minimize the cost of the culture medium?

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A firm's weekly profit (in dollars) in marketing two products is given by P=192x1+576x2x125x222x1x25000P = 192 x _ { 1 } + 576 x _ { 2 } - x _ { 1 } ^ { 2 } - 5 x _ { 2 } ^ { 2 } - 2 x _ { 1 } x _ { 2 } - 5000 where x1x _ { 1 } and x2x _ { 2 } represent the numbers of units of each product sold weekly. Estimate the average weekly profit when x1x _ { 1 } varies between 40 and 50 units and x2x _ { 2 } varies between 45 and 50 units.

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Use the regression capabilities of a graphing utility or a spreadsheet to find the least squares regression line for the points (10,2),(1,8),(6,9),(4,10),(16,4),(17,4)( 10,2 ) , ( 1,8 ) , ( 6,9 ) , ( 4,10 ) , ( 16,4 ) , ( 17,4 ) . Round your answer to three decimal places.

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The utility function U=f(x,y)U = f ( x , y ) is a measure of utility (or satisfaction) derived by a person from the consumption of two products x and y. Suppose the utility function is U=7x2+5xy2y2U = - 7 x ^ { 2 } + 5 x y - 2 y ^ { 2 } . Determine the marginal utility of product x.

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Evaluate the function w=x2yzxyzw = \frac { x ^ { 2 } - y z } { x y z } at (8,6,3)( - 8,6,3 )

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Use the function q(p1,p2)=7p19p29p1+9p2q \left( p _ { 1 } , p _ { 2 } \right) = \frac { 7 p _ { 1 } - 9 p _ { 2 } } { - 9 p _ { 1 } + 9 p _ { 2 } } to find q(5,8)q ( - 5 , - 8 )

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