已知x+y=3,xy=2,求 x²+xy+y²的值和(x-y)²

问题描述:

已知x+y=3,xy=2,求 x²+xy+y²的值和(x-y)²

x+y=3,xy=2,
x²+xy+y²
=x²+2xy+y²-xy
=(x+y)²-xy
=3²-2
=7
(x-y)²
=(x+y)²-4xy
=3²-4×2
=1