Proving with Congruence of intergers

[doggie_Walkes]

It just how do i prove that

b^3 +b^2 +1 does not divide by 5


Im thinking this way,
cause i know that b^3 +b^2 +1 is not congruent to 0(mod5)

therefore we use contradition to prove it. I am just not sure how to use contradition? or maybe I am looking at this in a completely bad light? maybe there is another method?

 

[robert Ihnot]

This can be worked out by considering all the cases from 0 to 4 mod 5.

 

[Mark44]

Double posted.