Đáp án:
$\text{$\dfrac{11x+1}{86}$ - $\dfrac{11x-1}{88}$ + $\dfrac{11x+2}{85}$ = $\dfrac{11x-2}{89}$}$
$\text{<=> $\dfrac{11x+1}{86}$ + 1 - $\dfrac{11x-1}{88}$+1 + $\dfrac{11x+2}{85}$ +1 = $\dfrac{11x-2}{89}$ +1 }$
$\text{<=> $\dfrac{11x+1}{86}$ + $\dfrac{86}{86}$ - $\dfrac{11x-1}{88}$ + $\dfrac{88}{88}$ + $\dfrac{11x+2}{85}$ + $\dfrac{85}{85}$ = $\dfrac{11x-2}{89}$ + $\dfrac{89}{89}$ }$
$\text{<=> $\dfrac{11x+87}{86}$ - $\dfrac{11x+87}{88}$ + $\dfrac{11x+87}{85}$ = $\dfrac{11x+87}{89}$}$
$\text{<=>(11x+87) . ($\dfrac{1}{86}$ - $\dfrac{1}{88}$ + $\dfrac{1}{85}$ - $\dfrac{1}{89}$) =0}$
$\text{<=>\(\left[ \begin{array}{l}11x+87=0\\\dfrac{1}{86} - \dfrac{1}{88} + \dfrac{1}{85} - \dfrac{1}{89}=0 (loại)\end{array} \right.\) }$
$\text{<=>11x +87=0 }$
$\text{<=>11x = -87}$
$\text{<=>x = $\dfrac{-87}{11}$ }$
$\text{Vậy phương trình có tập nghiệm S={$\dfrac{-87}{11}$} }$
