a
\(5^5-5^4+5^3=5^3\left(5^2-5+1\right)=5^3\cdot21⋮7\)
b
\(7^6+7^5-7^4=7^4\left(7^2+7-1\right)=7^4\cdot55⋮11\)
a)\(5^5-5^4+5^3\)
\(=5^3\left(5^2-5+1\right)\)
\(=5^3\times21⋮7\)
b) \(7^6+7^5-7^4\)
\(=7^4\left(7^2+7-1\right)\)
\(=7^4\times55⋮11\)
a, 55 - 54 + 53
= 53 . (25 - 5 + 1)
= 53 . 21 chia hết cho 7.
=> 55 - 54 + 53 chia hết cho 7. => đpcm.
b, 76 + 75 - 74
= 74 . (49 + 7 - 1)
= 74 . 55 chia hết cho 11
=> 76 + 75 - 74 chia hết cho 11 => đpcm.