Prove that angles in a triangle add up to 180 degrees
Early on at school you’re told that the sum of angles in a triangle add up to 180^{o}… but how can you be certain of this?
We use this to work out many other properties in shape, space and mathematics, it is important you know that why this is true and to not just take your teacher's word for it!
Proof
Imagine we have 2 parallel lines and we draw two lines going from the same point.
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We know angles on a straight line add up to 180^{o}, this does not have to be proved because it is by definition!
So, A+B+C = 180^{o}
Using alternate angles, as a property of parallel lines, we can label the two other interior angles of the triangle.
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Thus, the interior angles of a triangle sum up to 180^{o}.
This is just one of many ways to prove this.
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