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_数学解答

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

人气：109 ℃　时间：2020-04-12 14:33:14

解答

2x^2+2y^2
=2(x+y)^2 - 4xy
=14-8
=6
[x-y]^2
=(x+y)^2 - 4xy
=7-8
=-1