a) 8^5 + 8^4.2^4
= 8^4(8 + 16) chia hết cho 3
\(a,8^5+16^4=2^{15}+2^{16}=2^{15}\left(1+2\right)=2^{15}\cdot3⋮3\\ b,2^8+2^9+2^{10}=2^8\left(1+2+4\right)=2^8\cdot7⋮7\\ c,81^7-27^9-9^{13}=3^{28}-3^{27}-3^{26}=3^{26}\left(3^2-3-1\right)=3^{26}\cdot5=3^{22}\cdot3^4\cdot5=3^{22}\cdot405⋮405\\ d,12^{2n+1}+11^{n+2}=121\cdot11^n+12\cdot144^n=133\cdot11^n+12\left(144^n-11^n\right)\)
Mà \(\left(144^n-11^n\right)⋮\left(144-11\right)=133;133\cdot11^n⋮133\)
Do đó \(12^{2n+1}+11^{n+2}⋮133\)
b: \(2^8+2^9+2^{10}\)
\(=2^8\left(1+2+2^2\right)\)
\(=2^8\cdot7⋮7\)
