-would be- to draw another line and this is a bit of this proof wasn't obvious to me the first time that i thought about it so dont worry if its not obvious to you is that what happens is if we can continue this bisector - this angle bisector right over here so lets just continue it it just keeps going on and on and on and lets also maybe we can construct a similar triangle to this triangle over here if we draw a line that's parallel to AB down here so lets try to do that