已知x+y=5,xy=2,求下列各式的值 (1)x²+y² (2)(x-y)² 坑爹的数学题....

问题描述:

已知x+y=5,xy=2,求下列各式的值 (1)x²+y² (2)(x-y)² 坑爹的数学题....

x²+y²
=(x+y)²-2xy
=25-4
=21
(x-y)²
=x²+y²-2xy
==(x+y)²-4xy
=25-8
=17