x \(⋮\)12,21,28
\(\Rightarrow\)x \(\in\)BC ( 12,21,28 )
BCNN ( 12,21,28 ) = 84
\(\Rightarrow\)x \(\in\)B ( 84 ) = { 0 ; 84 ; 168 ; 252 ; 336 ; ... }
mà 150 < x < 300
\(\Rightarrow\) x \(\in\){ 168 ; 252 }
Theo đề bài: \(x⋮12,x⋮21,x⋮28\)
\(\Rightarrow x\in BC\left(12;21;28\right)\)
\(\Rightarrow x\in\left\{0;84;168;252;336;...\right\}\)
Mà \(150< x< 300\)
\(\Rightarrow x\in\left\{168;252\right\}\)
Vậy \(x\in\left\{168;252\right\}\).