Câu 1 :
Ta có : \(\frac{x}{4},\frac{x}{-6}\)
=> \(x\in BC_{\left(4,-6\right)}\)
=> \(\left\{{}\begin{matrix}x\in\left\{0,-4,4,8,-8,12,-12,16,-16,20,-20,....\right\}\\x\in\left\{0,6,-6,12,-12,18,-18,24,-24,.....\right\}\end{matrix}\right.\)
=> \(x\in\left\{0,12,-12,...\right\}\)
Mà \(-20< x< -10\)
=> \(x=-12\)
Vậy x = -12 .
Bài 2 :
Ta có : \(\frac{x}{-9},\frac{x}{12}\)
=> \(x\in BC_{\left(-9,12\right)}\)
=> \(\left\{{}\begin{matrix}x\in\left\{0,9,-9,18,-18,27,-27,36,-36,45,-45,....\right\}\\x\in\left\{0,12,-12,24,-24,36,-36,48,-48,60,-60,...\right\}\end{matrix}\right.\)
=> \(x\in\left\{0,36,-36,....\right\}\)
Mà \(20< x< 50\)
=> \(x=36\)
Vậy x = 36 .
