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9-5 Trigonometry and Area Essential Question: Is it possible to find the area of a triangle without knowing its height? **Remember the formula ½ ap ? The formula was easy to use if the apothem and radius formed 30-60-90 or 45-45-90 triangles, but what kind of triangles do octagons form? decagons? pentagons? Using trig., we can use the same formula on any regular polygon. Ex. Find the area of a regular pentagon with 8 cm. sides. Theorem 9-1 Area of a Triangle Given SAS The area of a B triangle is one half a c the product of the lengths of two A b C sides and the sine of the included Area of triangle angle. ABC = 1 bc(sin a ) 2 Ex. Find the area of the triangle. 34 km 28 39 km