Question

Answer 1

Bài 9:

\(Q=2n^2\left(n+1\right)-2n\left(n^2+n-3\right)\\ =Q=2n\left(n^2+n\right)-2n\left(n^2+n-3\right)\\ Q=2n\left(n^2+n-n^2-n+3\right)\\ =2n.3\\ =6n⋮6\)

Answer 2

Bài 52:

Đặt a =5k+1, b=5k+4\(\left(k\in N\right)\)

\(\Rightarrow ab+1=\left(5k+1\right)\left(5k+4\right)+1=25k^2+25k+5=5\left(5k^2+5k+1\right)⋮5\)