Đáp án:
`(x + 1)/10 + (x + 1)/11 + (x + 1)/12 = (x + 1)/13 + (x + 1)/14`
`⇔ (x + 1)/10 + (x - 1)/11 + (x + 1)/12 - (x + 1)/13 - (x + 1)/14 = 0`
`⇔ (x + 1) . (1/10 + 1/11 + 1/12 - 1/13 - 1/14)`
`⇔ x + 1 = 0` (vì `1/10 + 1/11 + 1/12 - 1/13 - 1/14 \ne 0`)
`⇔ x = 0 - 1`
`⇔ x = -1`
Vậy `x = -1`