（3X-5）/（X^2-2X-3）=(3x-5)/[(x-3)(x+1)]（3X-5）/（X2-2X-3）=A/（X-3）+B/（X+1）=[A(x+1)+B(x-3)]/[(x-3)(x+1)]=[(A+B)x+(A-3B)]/(x^2-2x-3)A+B=3A-3B=-5A=1 B=2
A=___1___,B=____2__
