代数计算2
问题描述：
代数计算2
已知x+y=7,xy=2,求：[1]2x^2+2y^2的值；[2][x-y]^2的值
答
2x^2+2y^2
=2(x+y)^2 - 4xy
=14-8
=6
[x-y]^2
=(x+y)^2 - 4xy
=7-8
=-1