已知25^x=2000,80^y=2000,求xy-x-y的值
问题描述：
已知25^x=2000,80^y=2000,求xy-x-y的值
答
因为25^x=2000 ,80^y=2000所以 (25^x)^y=2000^y ,(80^y)^x=(2000)^x即25^xy = 2000^y (1)80^xy = 2000^x (2)(1)*(2)得25^xy * 80^xy = 2000^y * 2000^x即 2000^xy = 2000^(y+x)即xy = x+y所以xy-x-y = xy-(x+y)=0...