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# Right triangle trig - how do you know?

I got my first dose of right triangle trigonometry today. The concept seems simple, but for some reason I can't grasp it easily. I just finished watching this video:

http://www.youtube.com/watch?v=dLOdHzttQ90

Can someone explain exactly why you would use sine in the first problem? or why you would choose to use sine, cosine or tangent in general as they pertain to the measurements you know and those you don't? I can understand and apply everything else but this. =\ We're working specifically on triangles with the measurements of one angle and one side given.

### 2 Answers

- 9 years agoFavorite Answer
These problems take a while to get used to, I used to be bad at them too. Anyways, he used sine in the first problem just by preference. To be honest you could've used any one of the 3, sine would just be the easiest. This is because if you want to find "X" which was the hypotenuse in this situation, you would've had to use cos or sin with cos being Adj/hyp and sin being opp/hyp, because of the fact that you are given the opposite side length it would make more sense to solve using sin rather figuring out the adjacent. So, basically because its less work. Hope that answers your question!

- TCLv 79 years ago
The video does a pretty good job of explaining the concepts. What trig. function; sin, cos or tan you use depends on what is given in the triangle and the definitions of those functions. Remember that

sin x = opp/hyp

cos x = adj/hyp

tan = hyp/adj