通分
[4(a-2)+(a+2)(a-2)[/(a+2)(a-2)=(a^2+4a-12)/(a+2)(a-2)=(a+6)(a-2)/(a-2)(a+2)=(a+6)/(a-2)通分[x^2-(x-1)(x-1)]/(x-1)=(x^2-x^+1)/(x-1)=1/(x-1)