Find the integral of xcos5x dx

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Homework Statement


Find the integral of xcos5x dx


Homework Equations


uv- (integral)vdu


The Attempt at a Solution



I tried to pick u=cos5x and dv=xdx, but the book uses u=x, dv=cos5x dx

Why can't my way work?
 
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fk378 said:
Why can't my way work?

It can. Generally, people choose the u and v so that the problem is simplified - the way the book chooses makes the integrand more tractable.
 

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