[tex]\displaystyle \int \dfrac{dx}{5x^2 -10x +15}\\\\\\=\displaystyle \int \dfrac{dx}{5(x^2-2x+3)}\\\\\\=\dfrac 1 5 \displaystyle \int \dfrac{dx}{x^2-2x+3}\\\\\\=\dfrac 15 \displaystyle \int \dfrac{dx}{x^2 -2x +1^2 -1 +3}\\\\\\=\dfrac 15 \displaystyle \int \dfrac{dx}{(x-1)^2+2}\\\\\\=\dfrac 15 \displaystyle \int \dfrac{du}{u^2 +\left(\sqrt 2 \right)^2}~~~~~~~~~;[x-1 =u \implies dx = du]\\\\\\\\[/tex]
[tex]=\dfrac 1 {5\sqrt 2} \tan^{-1} \left( \dfrac u{\sqrt 2}\right)+C~~~~~~;\left[\displaystyle \int \dfrac{dx}{a^2 +x^2} = \dfrac 1a \tan^{-1} \left( \dfrac xa \right) +C\right]\\\\\\=\dfrac{1}{5\sqrt 2} \tan^{-1} \left( \dfrac{x-1}{\sqrt 2}\right)+C[/tex]
