x的平方+x-6/x-3/x+3/x的平方-6-x
=(x+3)(x-2)/(x-3)×(x-3)(x+2)/(x+3)
=(x-2)(x+2)
=x²-4
x的平方+2xy+y的平方/xy-y的平方乘以x的平方-2xy+y的平方/xy+y的平方
=(x+y)²/y(x-y)×(x-y)²/y(x+y)
=(x+y)(x-y)/y²
=(x²-y²)/y²