“若(X+Y)的2次方=7,(X-Y)的2次方=5,求XY的值.”
问题描述:
“若(X+Y)的2次方=7,(X-Y)的2次方=5,求XY的值.”
答
(x+y)^2=7
(x-y)^2=5
(x+y)^2-(x-y)^2
=4xy=7-5
所以xy=1/2