You must be familiar with the:[br][br][b]sine rule[/b]: [math]\frac{a}{\sin A}=\frac{b}{\sin B}=\frac{c}{\sin C}=2R[/math][br][br][b]cosine rule[/b]: [math]a^2=b^2+c^2-2bc\cos A[/math]

You must be familiar with the identities [math]\frac{\sin x}{\cos x}=\tan x[/math] and [math]\sin^2x+\cos^2x=1[/math].[br][br]A trigonometric equation of the form [math]\cos x=0.5[/math] has many solutions:[list][*]a [b]principal [/b]solution, ie. [math]\cos^{-1}\left(0.5\right)=60^\circ[/math] - the one you get from your calculator;[/*][*]an [b]alternate [/b]solution, ie. [math]360^\circ-60^\circ=300^\circ[/math] - as cos has [i]two[/i] solutions in each 360°;[/*][*]an infinite number of [b]repeat[/b] solutions from [math]\pm360^\circ[/math], since cos repeats every 360°.[/*][/list][br]You will be asked to give the solutions in a certain interval, eg. [math]-180°\le x \le 180°[/math]