# AP Calculus AB

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The sum of x and y is 8. What is the maximum value of xy-x^2?

• AP Calculus AB -

f = x (y-x)
but y = 8-x
so
f = x (8-2x) = 8x - 2x^2
df/dx = 8 - 4 x
zero when x = 2

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