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
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
1: 2(X^2+Y^2)=2((X+Y)^2-2XY)=2(49-4)=90
2: =(X+Y)^2-4XY=49-8=41
答
2x^2+2y^2
=2(x+y)^2 - 4xy
=14-8
=6
[x-y]^2
=(x+y)^2 - 4xy
=7-8
=-1