计算题……帮忙算算~……………………急用
问题描述：
计算题……帮忙算算~……………………急用
计算:1.(a^2-4)/(a^2+4a+4)*2a/(a^2-4a+4)
2.(x^2y-x^3/x^2+2xy+y^2)/(x/x-y)*(x+y/x^2-2xy+y^2)
3.(x/(x-y)-x^2/(x^2-2xy+y^2))/(x/(x+y)-x^2/(x^2-y^2))
4.（x^2-x-2/(x^2-4x+4)-x/x^2-2x）*(x-4/x)
答
1.2a/(a^2-4)