Question

Chứng minh rằng:

3) (5^7- 5^6+ 5^5) chia hết cho 21

4) ( 7^6+ 7^5- 7^4) chia hết cho 77

Answer 1

3) (5⁷ - 5⁶ +5⁵) = 5⁵.(5²-5+1)= 5⁵.21 \(⋮\) 21

4) 7⁶+7⁵-7⁴= 7⁴.(7²+7-1)=7⁴.55=7³.7.11.4=7³.4.77 \(⋮\) 77

Answer 2

3) \(5^7-5^6+5^5=5^5.\left(5^2-5+1\right)=5^5.21⋮21\)

4) \(7^6+7^5-7^4=7^3.\left(7^3+7^2-7\right)=7^3.385=7^3.77.5⋮77\)