Problem 2
Prove that if , every quadrilateral that can be inscribed in a circle can be dissected into quadrilaterals each of which is inscribable in a circle.
Step 1 of 4: Use the cyclic criterion
In plain words
This criterion reduces the construction to matching angles.
Detailed analysis
A quadrilateral is cyclic exactly when a pair of opposite angles is supplementary. In particular, every isosceles trapezoid is cyclic.