已知xy=8满足x.x.y-x.y.y-x+y=56.求x.x+y.y的值_数学解答

已知xy=8满足x.x.y-x.y.y-x+y=56.求x.x+y.y的值

人气：406 ℃　时间：2019-10-20 00:00:49

解答

x.x.y-x.y.y-x+y
=xy(x-y)-(x-y)
=(xy-1)(x-y)
=7(x-y)=56
所以 x-y=8
x^2+y^2=(x-y)^2+2xy=64+16=80