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QuestionMathematics

Find the point(s) on the surface at which the tangent plane is horizontal. z= 9−x 2 −y 2 + 8y (x,y,z)=(…)
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Answer

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Step 1:
I'll solve this step by step, carefully following the LaTeX formatting guidelines:

Step 2:
: Find the partial derivatives

\frac{\partial z}{\partial y} = -2y + 8
To find points where the tangent plane is horizontal, we need to find where the partial derivatives with respect to x and y are both zero. Partial derivative with respect to x: Partial derivative with respect to y:

Step 3:
: Set partial derivatives to zero

-2y + 8 = 0
Set both partial derivatives equal to zero to find the critical points:

Step 4:
: Solve for x and y

y = 4
From the first equation: From the second equation:

Step 5:
: Calculate the z-coordinate

z = 25
Substitute x = 0 and y = 4 into the original equation:

Final Answer

The point where the tangent plane is horizontal is (0, 4, 25).