Question about trigonometric functions

Question

Started to learn trigonometric functions this week and I have a question.
When you are checking the x intercepts sometimes you can solve the equation with 2 or more different trigonometric identities, but some of the identities are not giving all of the solutions.
Is there a way to know which identity to use when there are a couple of options?

Answer 1

Which identity you use totally depends upon which side is given. If you only have an angle and the hypotenuse, using tan is useless as you don't have the opposite or adjacent. However, if you have two sides and an angle, you can use any trig ratio you want, as all of them will give you the right answer. Hope this answers your question?

Answer 2

This question would be clearer, and easier to answer, with an example.