A/(x-5)+B/(x+2)=[A(x+2)+B(x-5)]/[(x-5)(x+2)] =[(A+B)x+(2A-5B)]/[(x-5)(x+2)] ≡[5x-4]/[(x-5)(x+2)] A+B=5,2A-5B=-4, 解得A=3,B=2.
