Tìm số nguyên x biết: a) x : (-7) -6 = -15 b) x : 12 -12 = -37 c) x : (-25) +81 = 85

* Hướng dẫn giải

$\begin{array}{l}a) \text{x}:\left(-\text{7}\right)–\text{ 6 }=-\text{15}\\ \text{ x}:\left(-\text{7}\right)=-\text{9}\\ \text{x }=-\text{9}.\left(-\text{7}\right)\\ \text{x }=\text{ 63}\end{array}$

$\begin{array}{l}b)\text{x}:\text{ 12 }–\text{ 12 }=-\text{37}\\ \text{x}:\text{ 12 }=-\text{25}\\ \text{x }=-\text{25}.\text{12}\\ \text{x }=\text{3}00\end{array}$

$\begin{array}{l}c)\text{x}:\left(-\text{25}\right)+\text{ 81 }=\text{ 85}\\ \text{x}:\left(-\text{25}\right)=\text{ 4}\\ \text{x }=\text{ 4}.\left(-\text{25}\right)\\ \text{x }=-\text{1}00\end{array}$