and . Since 5 does not divide, .

Now we want to prove that 5 does not divide ab. Lets do what Jhevon has taught you before.... the contradiction method....

So let us assume 5 does divide ab, that means 5 divides . But this means 5 divides . But since and are both less than 5 and and nonzero, 5 cannot divide . Thiscontradictsour assumption that 5 divides ab. So 5 does not divide ab