# Integral Rule OR Trig Identity?

• Feb 24th 2009, 03:00 PM
gammaman
Integral Rule OR Trig Identity?
What exactly is the following. I have never attempted to integrate something with a polynomial in the denominator.

$\int\frac{1}{x^2+x+2}$
• Feb 24th 2009, 03:41 PM
Krizalid
First off, don't even think about it, that polynomial is irreducible on $\mathbb R,$ so we may find another way of solving such integral.

$\int{\frac{dx}{x^{2}+x+2}}=4\int{\frac{dx}{4x^{2}+ 4x+8}}=4\int{\frac{dx}{(2x+1)^{2}+7}}.$

Now put $2x+1=\sqrt7\tan\varphi.$