10.5 Trigonometry and Area• What is the area of a regular nonagon with 10-cm

sides?360

409

m PCR

1(40) 202

m PCS

5tan 20

a

5

tan 20a

1

2A ap

1 590

2 tan 20A

2618 .cm

Finding Area• A stop sign is a regular octagon. The standard size

has a 16.2-in. radius. What is the area of the stop sign to the nearest square inch?

36045

8

22.5m C cos22.5

16.2

a

16.2(cos22.5 ) a

sin 22.516.2

x

16(sin 22.5 ) x

8 2p x 8 2 16.2(sin 22.5 )p

259.2(sin 22.5 )

1

2A ap

116.2(cos22.5) 259.2(sin 22.5)

2

742.29241462742 .in

Area of a Triangle Given SAS

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

1(sin )

2Areaof ABC bc A

Finding Area• What is the area of the triangle?

112 21 sin 48

2A

93.63624801294 .cm

More Practice!!!!!

• Homework – Textbook p. 646 #6 – 18 EVEN.