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Unit 5 Lesson 5 Trigonometry and Area--

Find area of a regular nonagon with 10-cm sides and 20 degrees at the top of the isosceles triangle

Use sin, cos, and tan to find the apothem

Use tan 20=5/a. Then: a=5/tan 20.

Now, use A=1/2ap and substitute: = 1/2 5/tan 20 times 20

Theorem 10-8--

The area of a triangle is half the product of the lengths of two sides and the sine of the included angle