x-y-x2+2xy-y2+2=0 x+y=8 求xy?(x与y的积)
问题描述:
x-y-x2+2xy-y2+2=0 x+y=8 求xy?(x与y的积)
答
x-y-x2+2xy-y2+2=(x-y)-(x-y)^2+2=0 x
-y=2或-1 所以x=5 y=3或x=7/2 y=9/2
xy=15或xy=63/4