1,
Ta có:
`x\vdots12`
`=>x∈B(12)`
`=>x∈{12; 24; 36; 48; 60; 72; 84; ...}`
Mà `13<x<75`
`=>x∈{24; 36; 48; 60; 72}`
2,
`(x-6)^2=9`
`<=>(x-6)^2=3^2=(-3)^2`
`<=>`\(\left[ \begin{array}{l}x-6=3\\x-6=-3\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=9\\x=3\end{array} \right.\)