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