Câu hỏi :

Tìm \(ƯC\left( {45;25;105} \right) \)

A.  \(ƯC\left( {45;25;105} \right) = \left\{ {1;5;15} \right\}\)

B.  \(ƯC\left( {45;25;105} \right) = \left\{ {1;5;3;15} \right\}\)

C.  \(ƯC\left( {45;25;105} \right) = \left\{ {1;5} \right\}\)

D.  \(ƯC\left( {45;25;105} \right) = \left\{ {1;5;3} \right\}\)

* Đáp án

C

* Hướng dẫn giải

Ta có:

 \(\begin{array}{l} ƯC\left( {45;25;105} \right)\\ 45 = {3^2}.5\\ 25 = {5^2}\\ 105 = 3.5.7\\ \Rightarrow ƯCLN\left( {45;25;105} \right) = 5\\ \Rightarrow ƯC\left( {45;25;105} \right) = Ư\left( 5 \right) = \left\{ {1;5} \right\} \end{array}\)

Chọn C

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