1:
x^2y-xy^2-x+y=56
xy(x-y)-(x-y)=56
(xy-1)(x-y)=56
7(x-y)=56
x-y=8
x^2+y^2=(x-y)^2+2xy=8^2+2×8=80
2:a^2001+a^2000+a^1999
=a^1999(a^2+a+1)
=a^1999×0
=0
如有不明白,可以追问
如有帮助,记得采纳,谢谢
祝学习进步!
1:
x^2y-xy^2-x+y=56
xy(x-y)-(x-y)=56
(xy-1)(x-y)=56
7(x-y)=56
x-y=8
x^2+y^2=(x-y)^2+2xy=8^2+2×8=80
2:a^2001+a^2000+a^1999
=a^1999(a^2+a+1)
=a^1999×0
=0
如有不明白,可以追问
如有帮助,记得采纳,谢谢
祝学习进步!