\(x⋮\left(-9\right)\Rightarrow x⋮9\)
\(\Rightarrow x⋮9,12\Rightarrow x\in BC\left(9,12\right)\)
Ta có:
\(9=3^2\)
\(12=2^2\cdot3\)
\(\Rightarrow BCNN\left(9,12\right)=3^2\cdot2^2=36\)
\(\Rightarrow BC\left(9,12\right)\in\left\{0,36,72,108,...\right\}\)
Mà \(20< 36< 50\Rightarrow x=36\)
k mình nha