Question

E cần gấp

cmr 13^3 +1 chia hết cho 7

Answer 1

\(13^3+1=2197+1=2198\)

mà 2198 chia hết cho 7

⇒\(13^3+1\) chia hết cho 7

Answer 2

Ta có:

\(13\equiv-1\left(mod7\right)\)

\(\Rightarrow13^3\equiv\left(-1\right)^3\equiv-1\left(mod7\right)\)

\(\Rightarrow13^3+1\equiv-1+1\equiv0\left(mod7\right)\)

\(\Rightarrow\left(13^3+1\right)⋮7\left(đpcm\right)\)