I believe the first statement is false, because you can come up with a number divisible by 2 or by 6 that is not divisible by 12. To disprove a statement all you need a single counterexample, and in this case 6 should work as proof enough of a number that satisfies the conditions does not...
Homework Statement
This is a two part question, though once one is solved the other should be the same process:
"Write z=re^(it), where 0 < r < 1, in the summation formula and then with the aid of the theorem show that
\sum r^n*cos(nt) = (r cos (t) - r^2)/(1-2r*cos(t) + r^2)
when 0 < r < 1...