\(4a+5b+7c⋮11\Rightarrow5\left(4a+5b+7c\right)=20a+25b+35c=\)
\(11a+9a+22b+3b+33c+2c⋮11\) mà
\(11a+22b+33c⋮11\Rightarrow9a+3b+2c⋮11\Rightarrow3\left(9a+3b+2c\right)=\)
\(=27a+9b+6c=22a+\left(5a+9b+6c\right)⋮11\) mà \(22a⋮11\Rightarrow5a+9b+6c⋮11\left(dpcm\right)\)