已知(x+y)^2=3,(x-y)^2=7,则[(xy+2)(xy-2)-2x^2 y^2+4]÷1/2 xy的值为多少
问题描述：
已知(x+y)^2=3,(x-y)^2=7,则[(xy+2)(xy-2)-2x^2 y^2+4]÷1/2 xy的值为多少
要分析哦
答
(x+y)^2-(x-y)^2=3-7 4xy=-4 xy =-1
[(xy+2)(xy-2)-2x^2 y^2+4]÷1/2 xy=-2xy=-2*-1=2
所以结果是2