Question

chứng minh (3n - 4)*(6n +21) chia hết cho 3

Answer 1

\(\left(3n-4\right)\left(6n+21\right)\\ =18n^2+63n-24n-84\\ =18n^2+39n-84⋮3\\ \Rightarrow\left(3n-4\right)\left(6n+21\right)⋮3\left(dpcm\right)\)

Answer 2

theo bài ra ta có:

\(\left(3n-4\right)\left(6n+21\right)\\ =\left(3n-4\right)\left[3\left(2n+7\right)\right]\\ =3\left(3n-4\right)\left(2n+7\right)⋮3\\ \Rightarrow\left(3n-4\right)\left(6n+21\right)⋮3\left(đpcm\right)\)