Originally Posted by

**Tyro** So the formula for finding it has been explained to me as thus:

BD/DA=CE/EA

I understand the basis for this formula, what I struggle with is the item identification. So in the case of A=(-10,-4), and C= (8,5), find the y coordinate for B when x=-1. The example I'm given is as so

BD/(-1-(-10))=(5-(-4))/(8-(-10)), or more cleanly BD/9=9/18

It then breaks down to BD=9/2, which I understand. It then tells me since the B is higher than D (which makes 0 sense to me), that B is the y coord of D plus the length of BD, therefore -4+(9/2) (or 1/2).

Can someone help explain the item identification and the last part of why B is D+BD?