Yoshi's island style shooting mechanic

So I wanted to make something along the lines of the egg launching ability in Yoshi’s Island, but I’m not quite sure where to start.

Here’s a little diagram to help, in case you aren’t sure what I mean.

The user can hold the throw button to bring up a cursor that goes up and down in an arc over a 90 degree angle. Letting go of the button fires the object in the direction the cursor is facing.

I’m pretty decent at actionscript, but not so much math, so I would really appreciate any tips given about this subject :smiley:

Thanks

Brendan