求积分∫(2x+6/x^3+x-2)dx,求各位前辈赐教
1个回答

x³+x-2=x³-x²+x²-x+2x-2=x²(x-1)+x(x-1)+2(x-1)=(x-1)(x²+x+2)

则可设:(2x+6)/(x³+x-2)=A/(x-1)+(Bx+C)/(x²+x+2)

解得:A=2,B=C=-2

则:∫ (2x+6)/(x³+x-2) dx

=2∫ 1/(x-1) dx - ∫ (2x+2)/(x²+x+2) dx

=2ln|x-1| - ∫ (2x+1)/(x²+x+2) dx - ∫ 1/(x²+x+2) dx

=2ln|x-1| - ∫ 1/(x²+x+2) d(x²+x) - ∫ 1/[(x+1/2)²+(7/4)] dx

=2ln|x-1| - ln(x²+x+2) - (2/√7)arctan[(2x+1)/√7] +C