Question

x-y/x+y=(x-y)的平方/x的平方-y的平方（x不等于y）从左到右变形正确吗

Answer 1

(x-y)/(x+y)=(x-y)*(x-y)/[(x+y)*(x-y)]=(x-y)²/(x²-y²)

变形没有错,分母用了平方差公式.