Requesting a bit of help on the last part of my homework.

Need to prove that the following is a surjective homomorphism:

Let H and K be groups. Define the projection map:

: H x K H such that : (h, k) h

: H x K K such that : (h, k) k

How do you prove something is onto?

I know for a homomorphism you show that:

(ab) = (a)(b)

How would I attack this proof?

Please help!

Thanks.