(-2x2y)3*4x-3sup>=
问题描述：
(-2x2y)3*4x-3sup>=
x+y=4且x-y=10,则 2xy=
要求：写出详细解题思路,结果不重要,我需要的是过程.
Many thanks
答
题目1看不明白
解题目2
x+y=4,(x+y)^2=4^2=16,同样x-y=10,(x-y)^2=10^2=100,
(x+y)^2=x^2+2xy+y^2,
(x-y)^2=x^2-2xy+y^2,
(x+y)^2-(x-y)^2=4^2-10^2
(x^2+2xy+y^2)-(x^2-2xy+y^2)=16-100
4xy=-84
2xy=-42