通分:x+4/x^2-8x+15,x-5/x^2+x-12,x-3/x^2-x-20
问题描述：
通分:x+4/x^2-8x+15,x-5/x^2+x-12,x-3/x^2-x-20
答
x^2-8x+15=(x-3)(x-5) x^2+x-12=(x-3)(x+4) x^2-x-20=(x-5)(x+4)∴（x+4)/(x^2-8x+15)=(x+4)^2/(x-3)(x+4)(x-5)=(x^2+8x+16)/(x-3)(x+4)(x-5)（x-5)/(x^2+x-12)=(x-5)^2/(x-3)(x+4)(x-5)=(x^2-10x+25)/(x-3)(x+4)(x-...