*In the case where you have non-right-angled triangles, different methods are required to figure out the area and angles of the triangle.*

## Right-angled triangles

In the simple case of a right-angled triangle, the area is given by:

## Using the sin rule

If given the lengths of two sides of a triangle and also the angle joining the two sides the sine rule can be applied to determine the area of a triangle. For a triangle ABC with angles a,b & c shown below:

If lengths *c *and *b* are known and the angle A is known then the area of the triangle is:

## Heron’s formula

Given three lengths of a triangle, the area of that triangle can be determined. In Heron’s formula a special variable *s* is introduced. *s *is the semi-perimeter and is equal to:

The area of the triangle is therefore:

### Application

Find the area of the following triangle:

First, find the value of *s*

Then, use Heron’s formula

**See also:**

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