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# Urgent help

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Let \$ABCD\$ be a cyclic quadrilateral. Let \$P\$ be the intersection of \$\overleftrightarrow{AD}\$ and \$\overleftrightarrow{BC}\$, and let \$Q\$ be the intersection of \$\overleftrightarrow{AB}\$ and \$\overleftrightarrow{CD}\$. Prove that the angle bisectors of \$\angle DPC\$ and \$\angle AQD\$ are perpendicular.
Apr 7, 2019

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How do I prove that angle DCP equals 180 - angle DAB?

Apr 7, 2019
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Inscribed angles in a circle encompass an arc 2x their measure....opposite angles encompass the entire circle perimeter.

Say angle A is opposite angle B.....

then     2A + 2B = 360

2A = 360 - 2B

Divide throught by 2

A = 180-B                       Does that clear things up?

Apr 7, 2019