Angles in a triangle Look at triangle ABC shown below: c Photo credit: © Freddy Eliasson 2010, Shutterstock.com For any triangle, the interior angles.

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Presentation transcript:

Angles in a triangle Look at triangle ABC shown below: c Photo credit: © Freddy Eliasson 2010, Shutterstock.com For any triangle, the interior angles will add up to 180 How do we know this? How can we prove that this is true?

Interior angles in a triangle

Exterior angles of a triangle

Interior and exterior angles in a triangle Teacher notes Drag the vertices of the triangle to show that the exterior angle is equal to the sum of the opposite interior angles. Hide angles by clicking on them and ask pupils to calculate their sizes. Be aware that the angles are rounded to the nearest degree and that this may cause a slight error of ±1°.

Calculating angles