Finding the internal angles of 2D shapes. Week beginning 8th September 2025.
You know that there are 180 degrees in a triangle, 360 degrees in a quadrilateral. But how many degrees are in a pentagon? A hexagon? An octagon?
While we don't necessarily need to know these by heart, we do need to know how to calculate the internal angles in a 2D polygon if we are asked and there's a simple forumla to remember:
(Number of sides -2) x 180 degrees
So, for a pentagon, this would look like: (5-2) x 180 = 3 x 180= 540 degrees.
This works for all of the polygons you will need for your test so learn the equation by heart.
An alternative way is to split the shape into triangles and you'll see this method in our videos below.
Watch the videos at:
https://www.mathsisfun.com/geometry/interior-angles-polygons.html
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