I'm just guessing ...

Look at the question #8 where you are asked to build triangles. From the text of this question I assume that you should buildrighttriangles where the radius is the hypotenuse.

The radius is a kind of pointer (or the hand of a clock). You can adjust this pointer to a certain angle. Then the direction of this pointer is determined by the vertical (<-- that's the sine value) and horizontal part.