Question

Cho A= 999993¹⁹⁹⁹ - 555557¹⁹⁹⁷. Chứng minh rằng A chia hết cho 5.

Answer 1

Ta có:

\(A=999993^{1999}-555557^{1997}\)

\(A=999993^{1998}.999993-555557^{1996}.555557\)

\(A=\left(999993^2\right)^{999}.999993-\left(555557^2\right)^{998}.555557\)

\(A=\overline{\left(.....9\right)}^{999}.999993-\overline{\left(.....1\right)}.555557\)

\(A=\overline{\left(.....7\right)}-\overline{\left(.....7\right)}\)

\(A=\overline{\left(.....0\right)}\)

Vì A có tận cùng là 0

\(\Rightarrow A⋮5\) (Đpcm)