Angle Formulas
For a cyclic quadrilateral with successive sides a, b, c, d, semiperimeter s, and angle A between sides a and d, the trigonometric functions of A are given by
The angle θ between the diagonals satisfies
If the extensions of opposite sides a and c intersect at an angle , then
where s is the semiperimeter.
Read more about this topic: Cyclic Quadrilateral
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