# Math

posted by Dave

Evaluate the integral of x*(2x+5)^8*dx

I let u=2x+5 and du=2*dx, but then where do I go from there because I can't get rid of the x in order to integrate?

1. Steve

Let u = 2x+5
du = 2 dx
x = (u-5)/2

∫x(2x+5)^8 dx
= ∫(u-5)/2 * u^8 * du/2
= 1/4 ∫(u-5)u^8 du
= 1/4 ∫u^9 - 5u^8 du

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