Question

CMR: 8⁷ - 2¹⁸ chia hết cho 14

Answer 1

Ta có :

8⁷ - 2¹⁸ = ( 2³ )⁷ - 2¹⁸= 2²¹ -  2¹⁸ = 2¹⁸ ( 2³ - 1 ) = 2¹⁸ . 7 = 2¹⁷ .2.7 = 2¹⁷ . 14 ( chia hết cho 14 )

Vậy 8⁷-2¹⁸chia hết cho 14

Answer 2

\(8^7-2^{18}\)\(=\left(2^3\right)^7-2^{18}=2^{21}-2^{18}=2^{17}.2^4-2^{17}.2=2^{17}.\left(2^4-2\right)\)

                       \(=2^{17}.\left(2^4-2\right)=2^{17}.14\)