1.-x²-1/1-x=x²+1/x+1
2.m²/m-n+ n²/n-m=m²/m-n²/m-n=(m²-n²)/m-n=(m+n)(m-n)/m-n=m+n
3.a²+1/a-1 -a+1=a²+1/a-1 -(a-1)=a²+1/a-1 -(a-1)²/a-1=(a²+1 -a²+2a-1)/a-1=2a/a-1
4.x²/2-3x =-1 两边同乘以2-3x得 x²=-2+3x x²-3x +2=0 x=2或1