A) Provided we have a right angle (90") between two of the vectors. If we do, we use the trigonometric ratios: sin, cos or tan. To refresh your memory: sin 2 = opp / hyp hypotenuse opposite cos 2. = adj / hyp 2 adjacent tan ) = opp / hyp B) If we do not have a right angled triangle we use either the sine rule or the cosine rule. (It is rare that this type of question is asked in the matric examination.) 1. ) a b C sin A sin B sin C C 2.) a2 - b2 + c2 - 2bcCosA b A B C