Grade 10 Acute triangle trigonometry - Sine Law
Channel: Ms Havrot's Canadian University Math Prerequisites
Date: 2020-06-03

Proof of the Sine Law and an easy way to test to see if the Sine Law can be used to solve for a side length or angle.  I do examples showing both of the possible uses (two angles and one side and two sides and one angle opposite one of the sides).  
If you are asked to "solve" a triangle, that means that you are required to find all angles and all side lengths for the triangle. Always add any information that you know before you begin (i.e. three angles in a triangle add to 180 degrees can give you a third angle if you already have two)
Remember that your first "line of defence" is to use primary trig ratios, so you should look for that right angle first, then you check to see if the Sine Law will work and if not, well, that's the next lesson: COSINE LAW.