∫arctanx/x^2dx＝－∫arctanxd(1/x)＝－arctanx/x＋∫1/[x(1+x^2)]dx＝－arctanx/x＋∫[1/x－x/(1+x^2)]dx＝－arctanx/x＋ln[|x|/√(1+x^2)]＋C
∫x/√(x-3)dx＝2∫xd√(x-3)＝2x√(x-3)dx－2∫√(x-3)dx＝2x√(x-3)－2×2/3×√(x-3)^(3/2)＋C＝2/3×(x+6)√(x-3)＋C