Question
Question: 2<sup>3n</sup> –7n – 1 is divisible by...
23n –7n – 1 is divisible by
A
343
B
49
C
5
D
14
Answer
49
Explanation
Solution
23n = (1+ 7)n
23n = 1 + 7n + nC2 49 + nC3(7)3 + …….
Ž 23n – 7n –1 = 49 [nC2 + nC3 (7) +………]
which is divisible by 49