1、若x^2+y^2=5,xy=3,求(x+y)^2 (x-y)^2 2、x^+y^=5,x+y=6,求xy 3、若x+y=6,xy=3,求x^2+y^2 (x-y)^2
问题描述:
1、若x^2+y^2=5,xy=3,求(x+y)^2 (x-y)^2 2、x^+y^=5,x+y=6,求xy 3、若x+y=6,xy=3,求x^2+y^2 (x-y)^2
1、若x^2+y^2=5,xy=3,求(x+y)^2 (x-y)^2
2、x^+y^=5,x+y=6,求xy
3、若x+y=6,xy=3,求x^2+y^2 (x-y)^2
4、a+b=5,a-b=3,求ab
答
1.(x+y)²=x²+y²+2xy=5+2×3=11(x-y)²=x²+y²-2xy=5-2×3=-1 (题目有问题)2.xy=(1/2)[(x+y)²-(x²+y²)]=(1/2)(6²-5)=31/23.x²+y²=(x+y)²-2xy=6²...