Câu hỏi :

Tìm \(ƯC\left( {12;42;21} \right) \) 

A.  \(ƯC\left( {12;42;21} \right) = \left\{ {1;2;3;6} \right\}\)

B.  \(ƯC\left( {12;42;21} \right) = \left\{ {1;2;4} \right\}\)

C.  \(ƯC\left( {12;42;21} \right) = \left\{ {1;7} \right\}\)

D.  \(ƯC\left( {12;42;21} \right) = \left\{ {1;3;5;15} \right\}\)

* Đáp án

A

* Hướng dẫn giải

 \(\begin{array}{l} 12 = {2^2}.3\\ 42 = 2.3.7\\ 21 = 3.7\\ \Rightarrow ƯCLN\left( {12;42;21} \right) = 3 = 6\\ \Rightarrow ƯC\left( {12;42;21} \right) = Ư\left( 6 \right) = \left\{ {1;2;3;6} \right\} \end{array}\)

Copyright © 2021 HOCTAP247