1 câu trả lời
`1/x + 1/y = 1/3 + 1/xy`
`(x+y)/(xy) = 1/3 + 1/xy`
`(x+y-1)/(xy) = 1/3`
`xy = x+y-1`
`xy - x = y-1`
`x(y-1) = y-1`
`x(y-1) - y + 1 = 0`
`( x - 1 ) (y - 1) = 0`
`=> x -1 = 0 => x =1`
`=> y - 1 = 0 => y =1`
`#AC`
`1/x + 1/y = 1/3 + 1/xy`
`(x+y)/(xy) = 1/3 + 1/xy`
`(x+y-1)/(xy) = 1/3`
`xy = x+y-1`
`xy - x = y-1`
`x(y-1) = y-1`
`x(y-1) - y + 1 = 0`
`( x - 1 ) (y - 1) = 0`
`=> x -1 = 0 => x =1`
`=> y - 1 = 0 => y =1`
`#AC`
