(3x+4)/(x^2-x-2)=(3x+4)/[(x-2)(x+1)]
A/(x-2)-B/(x+1)=[A(x+1)-B(x-2)]/[(x-2)(x+1)]
=[(A-B)x+(A+2B)]/[(x-2)(x+1)]
对比,得
A-B=3
A+2B=4
解得
A=10/3 B=1/3
4A-B=40/3-1/3=13
(3x+4)/(x^2-x-2)=(3x+4)/[(x-2)(x+1)]
A/(x-2)-B/(x+1)=[A(x+1)-B(x-2)]/[(x-2)(x+1)]
=[(A-B)x+(A+2B)]/[(x-2)(x+1)]
对比,得
A-B=3
A+2B=4
解得
A=10/3 B=1/3
4A-B=40/3-1/3=13