Question

Chứng minh rằng 3^21 - 9^9 chia hết cho 13

 

Answer 1

\(3^{21}-9^9=3^{21}-3^{18}\)

\(=3^{18}\left(3^3-1\right)\)

\(=3^{18}.26\)

\(=3^{18}.2.13\)

\(\Rightarrow3^{21}-9^9⋮13\)

Answer 2

\(3^{21}-9^9=3^{21}-3^{18}\)

\(=3^{18}\left(3^3-1\right)=3^{18}.26\)

\(=3^{18}.2.13\)

\(\Rightarrow\)................