Tìm số nguyên x biết: a) (x-28) : (-12) = -5 b) (x+15) : (-28) = 8 c) (x+30) : (-45) = -14

* Hướng dẫn giải

$\begin{array}{l}a)\left(x-\text{28}\right):\left(-\text{12}\right)=-\text{5}\\ x-28=-\text{5}.\left(-\text{12}\right)\\ x-\text{28} =\text{ 6}0\\ x=\text{ 6}0+\text{28}\\ x=\text{ 88}\end{array}$

$\begin{array}{l}b)\left(x+\text{15}\right):\left(-\text{28}\right)=\text{ 8}\\ x+\text{15 }=\text{8}.\left(-\text{28}\right)\\ x+\text{15 }=-\text{ 224}\\ x=-\text{224 }–\text{ 15}\\ x=-\text{239}\end{array}$

$\begin{array}{l}c)\left(x+\text{3}0\right):\left(-\text{45}\right)=-\text{ 4}\\ x+\text{3}0=-\text{4}.\left(-\text{45}\right)\\ x+\text{3}0=\text{ 18}0\\ x=\text{18}0–\text{ 3}0\\ x=\text{15}0\end{array}$