已知x+y=10,xy=4,求x²+y²和（x-y）²的值

题目

已知x+y=10,xy=4,求x²+y²和（x-y）²的值

答案

x²+y²
=(x+y)²-2xy
=10²-2*4
=100-8
=92
(x-y)²
=(x+y)²-4xy
=10²-4*4
=100-16
=84