Basically, geometry screws with your mind. It's tough, but you have to imagine these triangles set up next to each other, or use your finger to trace to the different points, that way you can situate yourself.
So, there are three triangles, ΔCAD, ΔBCD, and ΔBAC. and they're all similar. this would be the answer to your first question. (If you need help finding them, use the methods I mentioned earlier :))
Now, to figure out the proportions, look at which sides are the same (not literally, but size wise. Like, the hypotenuse is always the 2nd longest, the bottom is the longest, and the side is the shortest.
CD and BD go together because #1 the letters go from the top tip of the Δ to the bottom where they meet the bottom side. Now, as for AD, that's the hypotenuse. So, you find another hypotenuse from the other two triangles. (The other two are AC and CB).
the last one heey put that CA and BA are proportionate. CA and BA happen to both be bottoms of Δ's. then they put AC. AC is both a hypotenuse and a bottom, so you have a variety of sides you could go with. (hypotenuses:AD, CD, bottoms:AB, and CB)
I hope this helps!
