Indefinite integral

∫ ydy / (y²+1)

Let u = y²+1

du/dy = 2y

du = 2ydy　　　ydy = (1/2)du

∫ ydy / (y²+1) = (1/2)∫ du/u

=(1/2)ln(u) + C

= (1/2)ln(y²+1) + C

Mr. Kowk的回答較好