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Learn how to use the lengths of the sides of a right triangle to find trigonometric ratios, solve applied problems, and determine missing parts of the triangle. Explore the concepts of sine, cosine, and tangent ratios with practical examples.
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CHAPTER 10 Geometry
10.6 • Right Triangle Trigonometry
Objectives Use the lengths of the sides of a right triangle to find trigonometric ratios. Use trigonometric ratios to find missing parts of right triangles. Use trigonometric ratios to solve applied problems.
Ratios in Right Triangles • Trigonometry means measurement of triangles. • Trigonometric Ratios: Let A represent an acute angle of a right triangle, with right angle, C, shown here.
Ratios in Right Triangles • For angle A, the trigonometric ratios are • defined as follows:
Example: Becoming Familiar with The Trigonometric Ratios Find the sine, cosine, and tangent of A. Solution: Using the Pythagorean Theorem, find the measure of the hypotenuse c.
Example: Finding a Missing Leg of a Right Triangle • Find a in the right triangle • Solution: Because we have a known angle, 40°, with a known tangent ratio, and an unknown opposite side, “a,” and a known adjacent side, 150 cm, we can use the tangent ratio. • tan 40° = • a = 150 tan 40° ≈ 126 cm
Applications of the Trigonometric Ratios • Angle of elevation: Angle formed by a horizontal line and the line of sight to an object that is above the horizontal line. • Angle of depression: Angle formed by a horizontal line and the line of sight to an object that is below the horizontal line.
Example: Problem Solving using an Angle of Elevation • Find the approximate height of this tower. • Solution: We have a right triangle with a known angle, 57.2°, an unknown opposite side, and a known adjacent side, 125 ft. • Using the tangent ratio: • tan 57.2° = • a = 125 tan 57.2° ≈ 194 feet
Example: Determining the Angle of Elevation • A building that is 21 meters tall • casts a shadow 25 meters long. • Find the angle of elevation of the • sun. • Solution: We are asked to • find mA.
Example continued • Use the inverse tangent key • The display should show approximately 40. Thus the angle of elevation of the sun is approximately 40°.