19 has come up twice in the past few years meaning that it is less likely to come up. Hopefully it'll be 4,6 or 9 but that seems to be unlikely. We'd be so unlucky if we did get 14.

I think that it may be theorem 14. I found this video very helpful when studying the theorem. The only thing that he doesn't explain is why triangles ACB and ADC are similar. But this will only be worth a couple of marks in the exam. Here is the link to the video:
https://www.youtube.com/watch?v=LrS5_l-gk94
Hope this helps :)

lucyc57— 12/06/16