∫x/【(x^2+1)(x^2+4)】dx=½ ∫1/[(x²+1)(x²+4)]d(x²)=1/6 ∫[1/(x²+1) -1/(x²+4)] d(x²)=1/6 [ln(x²+1) -ln(x²+4)]+C=1/6 ln[(x²+1)/(x²+4)] +C
