Đáp án: x = -2
Giải thích các bước giải:
$\dfrac{x + 2}{21}$ + $\dfrac{x + 2}{22}$ + $\dfrac{x + 2}{23}$ = $\dfrac{x + 2}{27}$ + $\dfrac{x + 2}{28}$
⇔ $\dfrac{x + 2}{21}$ + $\dfrac{x + 2}{22}$ + $\dfrac{x + 2}{23}$ - $\dfrac{x + 2}{27}$ - $\dfrac{x + 2}{28}$ = 0
⇔ (x + 2) ($\dfrac{1}{21}$ + $\dfrac{1}{22}$ + $\dfrac{1}{23}$ - $\dfrac{1}{27}$ - $\dfrac{1}{28}$ )= 0
mà $\dfrac{1}{21}$ + $\dfrac{1}{22}$ + $\dfrac{1}{23}$ - $\dfrac{1}{27}$ - $\dfrac{1}{28}$ $\neq$ 0
`⇔ x + 2 = 0`
`⇔ x = -2`
Vậy `x = -2`