Question

CMR n tự nhiên

a) \(\left(5n+2\right)^2-4⋮5\)

b) \(\left(4n+1\right)^2-1⋮8\)

Answer 1

a) Ta có: \(\left(5n+2\right)^2-4\)

\(=\left(5n+2-2\right)\left(5n+2+2\right)\)

\(=5n\left(5n+4\right)⋮5\)

b) Ta có: \(\left(4n+1\right)^2-1\)

\(=\left(4n+1-1\right)\left(4n+1+1\right)\)

\(=4n\left(4n+2\right)\)

\(=8n\left(2n+1\right)⋮8\)