Question

Chung minh: (n-3)(n+3)-(n-7)(n-3) chia het cho 10.

MInh can gap. Cac ban giup minh voi. Minh like cho.

Answer 1

Ta có:(n-3)(n+3)-(n-7)(n-3)             (1)

        =(n-3)(n+3-n+7)

        =10(n-3)

Vậy PT(1) chia hết cho 10

Answer 2

\(\left(n-3\right)\left(n+3\right)-\left(n-7\right)\left(n-3\right)=\left(n-3\right)[n+3-\left(n-7\right)]\)

\(=\left(n-3\right)\left(n+3-n+7\right)=\left(n-3\right)\cdot10⋮10\)(ĐPCM)