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f(x) = x^2 + 9x - 2 | Note: use of " ^ "
DQ =
f(x+h) = (x+h)^2 + 9(x+h) -2 = x^2 + 2xh + h^2 + 9x + 9h - 2
f(x+h) - f(x) = x^2 + 2xh + h^2 + 9x + 9h - 2 -x^2 - 9x + 2
= (2xh + h^2 + 9h)/h = 2x + h + 9
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