x+2+4/x-2;
=(x²-4+4)/(x-2)
=x²/(x-2)
(a-1/1-a)÷(a^2-a+1/a^2-2a+1);
=(a-a²-1)/(1-a)÷(a²-a+1)/(a-1)²
=(a²-a+1)/(a-1)÷(a²-a+1)/(a-1)²
=a-1
( m +mn/m-n)÷（m-mn/m+n);
=(m²-mn+mn)/(m-n)÷(m²+mn-mn)/(m+n)
=(m+n)/(m-n)
(a/a+1+ 1)÷(1- 3a^2/1-a^2)
=(a+a+1)/(a+1)÷(1-a²-3a²)/(1-a²)
=(2a+1)/(a+1)÷(1-2a)(1+2a)/(1-a)(1+a)
=(1-a)/(1-2a)
又是我帮你回答的.呵呵