How do you evaluate the integral int ln(x^2+x^3)ln(x2+x3)?

1 Answer
Jan 14, 2017

xln(x^2+x^3)+ln(abs(x-1))-3x+Cxln(x2+x3)+ln(|x1|)3x+C

Explanation:

We have the integral:

I=intln(x^2+x^3)dxI=ln(x2+x3)dx

We should apply integration by parts, which takes the form intudv=uv-intvduudv=uvvdu. Where intln(x^2+x^3)dx=intudvln(x2+x3)dx=udv, let u=ln(x^2+x^3)u=ln(x2+x3) and dv=dxdv=dx.

Differentiating uu and integrating dvdv gives:

{(u=ln(x^2+x^3)" "=>" "du=(2x+3x^2)/(x^2+x^3)dx=(2+3x)/(x+x^2)dx),(dv=dx" "=>" "v=x):}

So:

I=uv-intvdu

I=xln(x^2+x^3)-int(2x+3x^2)/(x+x^2)dx

I=xln(x^2+x^3)-int(2+3x)/(1+x)dx

Either perform long division on (3x+2)/(x+1) or do the following rewriting: (3x+2)/(x+1)=(3(x+1)-1)/(x+1)=3-1/(x-1). So:

I=xln(x^2+x^3)-(3intdx-intdx/(x-1))

I=xln(x^2+x^3)-(3x-ln(abs(x-1)))

I=xln(x^2+x^3)+ln(abs(x-1))-3x+C