Question

[điên123]

CMR

a,a²(a+1)+2a(a+1) chia hết cho 6 \(\forall a\in Z\)

b,a(2a-3)-2a(a+1)\(⋮5\forall a\in Z\)

Answer 1

[Đặng Tú Phương]

a,\(a^2\left(a+1\right)+2a\left(a+1\right)=\left(a^2+2a\right)\left(a+1\right)\)

\(=a\left(a+2\right)\left(a+1\right)⋮3⋮2\)

                                               \(⋮6\left(ĐPCM\right)\)

b,\(a\left(2a-3\right)-2a\left(a+1\right)\)

\(=2a^2-3a-2a^2-2a\)

\(=-5a⋮5\left(ĐPCM\right)\)