1.(x-1+x/1-x)(2/1+x²-1)=(1-x²-1-x)/(1-x)÷(2-1-x²)/(x²+1）=-x(x+1)/(1-x)×(x²+1)/(1+x)(1-x)=-(x²+1)/(1-x)² 2.（3/a-2+12/a²-4）÷（2/a-2-1/a+2）=(3a+6+12)/(a+2)(a-2)÷(2a+4-a+2)/(a+2)(a-2)=3
