Newton's Second Law of Motion

I learned many things about Newton's Second Law. I learned that an object's velocity will change if it is pusshed or pulled by another object. I didn't find too much dificulty with this section because of the stuff we had learned earlier was very similar. Finding friction was something that was a little hard at first but then I found it quite easy. I just had to do a ∑Fx=... , and once I figured out how to do that it became very easy. But, the only thing that was a little difficult were solving for forces at an angle, I still get confused a bit about when to use cos or sin. I think I need to work better on solving things at an angle. I am pretty good at finding any other forces.

(Sorry for posting about an hour later, I have internet problems at the wort of times.)