Question

a, 7^6+7^5+7^4 chia hết cho 55

b, 16^5+2^5 chia hết cho 33

c, 81^7 - 27^9 - 9^13 chia hết ch0 405

 

Answer 1

bài chứng minh à

Answer 2

chuẩn '

Answer 3

a) \(7^6+7^5+7^4=7^4\left(7^2+7+1\right)=7^4.57\) chia hết cho 57 (đpcm)

b) \(16^5+2^{15}\)

\(=\left(2^4\right)^5+2^{15}\)

\(=2^5.2^{15}+2^{15}\)

\(=2^{15}\left(2^5+1\right)=2^{15}.33\) chia hết cho 33 (đpcm)

c) \(81^7-27^9-9^{13}\)

\(=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}\)

\(=3^{28}-3^{27}-3^{26}\)

\(=3^{26}\left(3^2-3-1\right)\)\(=3^{26}.5=3^{22}.3^4.5=3^{22}.405\)chia hết cho 405 (đpcm)