My problem is that I believe I have a wrong concept somewhere, and I can't find what I'm doing wrong exactly. For this problem let's suppose what I want to do is find the rectangular coordinates of BC. I had two "possible solutions" I tried to achieve this, . First the correct one: (I apologize by drawing quality) By determining angles I can find that the angle between the vertical axis and BC is, therefore: [itex](300\sin(50),300\cos(50))[/itex] Now the wrong one: By looking at the original figure alone, first I project BC into AB, then project BC into either X axis or Y axis. Procedure: Projecting BC into AB -> [itex](300\sin(20),300\sin(20))[/itex] Projecting my new AB' into X and Y axis -> [itex]((300\sin(20))\sin(60),(300\sin(20))\cos(60))[/itex] So, why is my second procedure wrong?