Let me show you a method that requires little calculation Let √(x^2+1)=y, then xdx=ydy, dx/y = dy/x, which is also equal to d(x+y)/(y+x) The given integral is ∫ydx = xy - ∫x(dy/dx)dx = xy - ∫x(x/y)dx =xy - ∫(y^2-1)/ydx = xy - ∫ydx + ∫dx/y therefore , 2∫ydx = xy +∫dx/y As mentioned before, dx/y = dy/x = d(x+y)/(y+x) So ∫dx/y = ∫d(x+y)/(y+x) = log(x+y) Finally, ∫ydx = 1/2(xy +log(x+y) = 1/2 ( x√(x^2+1) + log (x + √(x^2+1))