Question

HELP
if a+1 is divisible by 3 prove that 4+7a is divisible by 3 too

Answer 1

Explanation:

Assume there exists integer k such that 3k=a+1.

4+7a

=7a+4

=7(a+1)-3

=7(3k)-3

=3(7k-1)

This implies that if there exists integer k such that 3k=a+1 then there is integer 7k-1 such that 3(7k-1)=4+7a