[nerd434]

N/A

[notnek]

There's quite a lot to explain so it's probably best for you to google an explanation of the method - I'm sure there are thousands.

Or you could post an example question

[TenOfThem]

1. Draw the triangle
2. Label the sides O,H,A
3. Decide which 2 sides are involved in your calculation
4. Write down the formula
5. Substitute in the appropriate numbers
6. You will have one of the following
7. Unknown angle ... use inverse function
8. Unknown side ... use standard algebraic re-arrangement to solve