The form you should use may be given to you in a question, but if not, any one will do. If in doubt, \(k\cos (x - \alpha )\) usually works. These worked examples show the processes you'll need to go ...

Calculate the length AB. Give the answer to one decimal place. Label the sides of the triangle \(o\), \(a\) and \(h\). Next choose the correct ratio from \(s^o_h~c^a_h~t^o_a\). The length \(h\) is ...