9000045706 | math4u.vsb.cz

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9000045706

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Given a regular pentagon with the side

a

, find the radius

r

of the circle circumscribed to this pentagon.

r = \frac{a}{2 \cdot \cos 54^{\circ}}

r = \frac{2 a}{\cos 72^{\circ}}

r = \frac{2 a}{\cos 54^{\circ}}

r = \frac{a}{2 \cdot \cos 72^{\circ}}