Area of a triangle
If you can find the area of a rectangle, you can quickly work out how to find the area of a triangle.
A triangle is simply half of a rectangle. You can try this yourself (or watch me doing it here) by getting a piece of paper and cutting it in half along one diagonal. You should now have two triangles, each half of the original piece of paper.
So the area of a triangle is half of the area of the rectangle surrounding it.
We tend to use base and height instead of length and width when working with triangles - this doesn't change the method though!
You must take care to always use two measurements that are perpendicular (at right angles) to each other. You could even draw a rectangle around the triangle to make sure you have done this correctly.