(a+2/a²-2a-a-1/a²-4a+4)÷a-4/a
=[(a+2)/a(a-2) -(a-1)/(a-2)² ]× a/(a-4)
=(a-4)/a(a-2)² ×a/(a-4)
=1/(a-2)²
解下列方程：
x/x-2-1/x²-4=1
x(x+2)-1=x²-4
x²+2x-1=x²-4
x=-3/2
2x+1/x-1+6/x²-1=2
(2x+1)(x+1)+6=2(x²-1)
2x²+3x+7=2x²-2
3x=-9
x=-3分解因式（a²+4）²-16a²（a²+4）²-16a²=（a²+4）²-(4a)²=（a²+4+4a）（a²+4-4a）=(a+2)²(a-2)²