1）x²-4分之x,（x+2)²分之x-1 (通分）

1）x²-4分之x,（x+2)²分之x-1 (通分）
x/(x²-4)=x/(x-2)(x+2)=x(x+2)/(x-2)(x+2)²
(x-1)/(x+2)²=(x-1)(x-2)/(x-2)(x+2)²
2）2x+3分之1,3-2x分之2,4x²-9分之2x+5 （通分）
1/(2x+3)=(2x-3)/(2x+3)(2x-3)
2/(3-2x)=-2/(2x-3)=-2(2x+3)/(2x+3)(2x-3)
(2x+5)/(4x²-9)=(2x+5)/(2x+3)(2x-3)
3）a-b,a-b分之b,a²-b²分之1 （通分）
a-b=(a-b)(a+b)(a-b)/(a+b)(a-b)=(a+b)(a-b)²/(a+b)(a-b)
b/(a-b)=b(a+b)/(a+b)(a-b)
1/(a²-b²)=1/(a+b)(a-b)
4）计算 x+3分之1+6-2x分之1-2x²-18分之3x-15
1/(x+3)+1/(6-2x) -(3x-15)/(2x²-18)
=2(x-3)/[2(x+3)(x-3)]-1/[2(x-3)]-(3x-15)/[2(x+3)(x-3)]
=2(x-3)/[2(x+3)(x-3)]-(x+3)/[2(x+3)(x-3)]-(3x-15)/[2(x+3)(x-3)]
=[2(x-3)-(x+3)-(3x-15)]/[2(x+3)(x-3)]
=[2x-6-x-3-3x+15]/[2(x+3)(x-3)]
=[2x-x-3x-6-3+15]/[2(x+3)(x-3)]
=[-2x+6]/[2(x+3)(x-3)]
=-2(x-3)/[2(x+3)(x-3)]
=-1/(x+3)