We have shown that the angle sum of a triangle is . We have also shown that the measure of an inscribed angle is half the measure the central angle that intercepts the same arc. In this post, we use the Inscribed Angle Theorem to show that the Triangle Angle Sum Theorem holds. Theorem The […]

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# Posts tagged with 'triangle angle sum'

## Proof of Angle Sum of Quadrilaterals

Introduction We have learned that the angle sum of a triangle is . What about the quadrilaterals? The square and the rectangles have four right angles, so clearly, the sum of their interior angles is . But what about other quadrilaterals? Before proceeding with the proof, to those who want to explore first, draw different […]

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## Triangle Angle Sum Theorem: A More Friendly Proof

Introduction In high school mathematics, we were taught to write proofs in two columns. There are some proofs however that are easier to understand if we use Algebra. The triangle angle sum theorem that I have posted yesterday can be proven algebraically. Its proof which I think is easier to understand is shown below. Theorem […]

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