Note: the angles are labelled with a capital letter and the sides are labelled with a lower-case letter. The diagram below shows the formulas that we need to calculate the missing angle or side using the sin rule.
Let’s try an example to calculate a missing angle. So, we have to use the formula.
Rearrange the formula to have on its own.
In the calculator, press to find . °
The cosine rule can also be used to calculate missing lengths and angles.
Below shows the formulas for the cosine rule. The ones on the left are used to find missing lengths, the ones on the right are used to work out missing angles.
Substitute in the relevant figures to find the missing length or angle.
Exact trigonometric values: