解答如下:
1/x + 4/y = 4/4x + 4/y = (x + y)/ 4x + (x + y)/y
= 1/4 + y/4x + x/y + 1
≥ 5/4 + 1 = 9/4
当且仅当y/4x = x/y,即x =4/3,y = 8/3时,取到等号
解答如下:
1/x + 4/y = 4/4x + 4/y = (x + y)/ 4x + (x + y)/y
= 1/4 + y/4x + x/y + 1
≥ 5/4 + 1 = 9/4
当且仅当y/4x = x/y,即x =4/3,y = 8/3时,取到等号