An isosceles trapezoid is a trapezoid whose sides are congruent. An example of an isosceles trapezoid is shown below. The trapezoid is isosceles with parallel to and congruent to . In this post, we are going to show that the diagonals of an isosceles trapezoid are congruent. In the figure below, we will show that […]

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# Posts tagged with 'mathematical proof'

## The Proof of the Second Case of the Inscribed Angle Theorem

In December last year, we have proved one case of the Inscribed Angle Theorem. In this post, we prove the second case. Note that the order of the cases does not matter; we just placed ordinal numbers to distinguish one from the other. Recall that the first case of the theorem involved drawing an auxiliary […]

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## Quadrilaterals with Congruent Opposite Angles are Parallelograms

In last week’s post, we have learned that quadrilaterals with congruent opposite sides are parallelograms. In this post, we show a related theorem. That is, quadrilaterals whose opposite angles are congruent are parallelograms. In the figure above, is a quadrilateral where and are congruent and and are congruent. In proving the theorem, we need to […]

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