Sine&Cosine Rule

We can use trigonometry to work out a missing side or angle in a right angled triangle.

**for example:**

if a right angled triangle's opposite and adjacent sides are of the same length then the missing angle **must** be 45^{o}

Often in real life situations th triangle is not right angled.

When this is the case we can use the sine and cosine rules.

The sine rule

the rule is:

$a/sinA = b/sinB = c/sinC$

this rule allows us to work out any missing side or angle provided we know some of the lengths and angles in the triangle.

So suppose we know that angle A in the triangle above is 45^{o}, that angle B is 30^{o} and that the length b is 2cm.

Can you work out the remaining angle C and the lengths a and c?

page revision: 4, last edited: 05 Jul 2007 10:17