∫（x+1）/（x^2+2x+3）dx=1/2∫2（x+1）/(x^2+2x+3)dx =1/2∫1/(x^2+2x+3)d(x^2+2x+3)=1/2ln(x^2+2x+3)
∫（x+1）/（x^2+2x+3）dx=1/2∫2（x+1）/(x^2+2x+3)dx=1/2∫1/(x^2+2x+3)d(x^2+2x+3)=1/2ln(x^2+2x+3)
