Previously this document introduced Trigonometry and focussed on right angles triangles, to bring in Pythagoras Theorem and some basic ‘Trig Identities’.


Pythagoras Theorem works only for triangles with one ‘right angle’, but of course there are other sorts of triangles such as equilateral, scalene and isosceles that don’t have any internal 900 angles, so what about these?


It’s not a case of SOH CAH TOA here, there is a rule for finding side lengths and internal angles, in fact two rules known respectively as the SINE rule and the COSINE rule, effectively extensions of the Pythagoras Theorem.


The two rules are quite straightforward. To establish which of the two to use will depend on the information you are given in the question: