已知3x加4除以x的平方減x減2等于A除以x減2的商減B除以x加1,A,B為常數(shù)
(3x+4)/(x^2-x-2)=A/(x-2)-B/(x+1)
(3x+4)/(x-2)(x+1)=(A(x+1)-B(x-2))/(x-2)(x+1)
(3x+4)/(x-2)(x+1)=((A-B)x+A+2B)/(x-2)(x+1)
A-B=3
A+2B=4
解得
A=10/3
B=1/3
4A-B=4*10/3-1/3=13