Question

cho 2a+7b chia hết cho 3. CM 4a+2b chia hết cho 3

Answer 1

Vì  \(2a+7b⋮3\)

\(\Rightarrow2.\left(2a+7b\right)⋮3\)

\(\Rightarrow4a+14b⋮3\)

\(\Rightarrow4a+2b+12b⋮3\)

Mà \(12b⋮3\Rightarrow4a+2b⋮3\left(Đpcm\right)\)

Chúc bạn học tốt !!! 

Answer 2

Ta có: \(2a+7b=2a+b+6b⋮3\)

\(\Rightarrow2a+b⋮3\)(vì \(6b⋮3\))

\(\Rightarrow2\left(2a+b\right)=4a+2b⋮3\)