I need help with a simple integration...

hammy

New member
Joined
Jul 4, 2011
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13
I don't know why I can figure this one out.

I need to integrate ((x)^3)ln(8x)
using the form:

((u)^n)ln(u)du = (((u)^(n+1))/((n+1)^2))*[(n+1)lnu-1]+c

I just don't know what to make u equal to make the u/du substitution to match the form
 
hammy said:
I don't know why I can figure this one out.

I need to integrate ((x)^3)ln(8x)
using the form:

((u)^n)ln(u)du = (((u)^(n+1))/((n+1)^2))*[(n+1)lnu-1]+c

I just don't know what to make u equal to make the u/du substitution to match the form

One way:

u = 8x

Be careful about rest of the substitution....

What does x[sup:13se7dh6]3[/sup:13se7dh6]ln(8x) dx become - with that substitution?
 
Aight, so now I can make it (1/8)u = x then just cube that and carry on?
 
hammy said:
Aight, so now I can make it (1/8)u = x then just cube that and carry on?

yes and don't forget about converting "dx".
 
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