∫x/（x^2+3x+3）dx =∫(x+3/2-3/2)/（x^2+3x+3）dx =∫(x+3/2)/（x^2+3x+3）dx-3/2∫dx/（x^2+3x+3) =1/2∫d(x^2+3x+3)/（x^2+3x+3）-3/2∫dx/（x+3/2)^2+（√3/2）^2 =ln(x^2+3x+3)/2-√3arctan(√3x/2)+C
