Explain why any parallelogram that is inscribed in a circle must be a rectangle. Draw pictures and think about the properties of both cyclic quadrilaterals and parallelograms.

Explanation:

Opposite angles of an inscribed quadrilateral are supplementary. Opposite angles of a parallelogram are congruent. Supplementary angles that are congruent must be 90°. Hence an inscribed parallelogram must be a rectangle.

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since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.