x+y=20 x^2-y^2=20 求x-y怎么解

问题描述:

x+y=20 x^2-y^2=20 求x-y怎么解
20(x-y)=20
哪里来的

x^2-y^2=20
(x+y)(x-y)=20
20(x-y)=20
x-y=1