AP Calculus AB

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

Please help!

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  1. 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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    posted by Damon

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