Learn to solve, verify, and find extraneous solutions in trigonometric equations, with practical examples and in-depth explanations to enhance your understanding.
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Five-Minute Check (over Lesson 13–4) CCSS Then/Now New Vocabulary Example 1: Solve Equations for a Given Interval Example 2: Infinitely Many Solutions Example 3: Real-World Example: Solve Trigonometric Equations Example 4: Determine Whether a Solution Exists Example 5: Solve Trigonometric Equations by Using Identities Lesson Menu
Content Standards F.TF.8 Prove the Pythagorean identity sin2 (θ) + cos2 (θ) = 1 and use it to find sin (θ), cos (θ), or tan (θ) given sin (θ), cos (θ), or tan (θ) and the quadrant of the angle. Mathematical Practices 4 Model with mathematics. 6 Attend to precision. CCSS
Solve Equations for a Given Interval Solve 2cos2 – 1 = sin if 0≤ 180. 2cos2 – 1 = sin Original equation 2(1 – sin2 ) – 1 – sin = 0 Subtract sin from each side. 2 – 2 sin2 – 1 – sin = 0 Distributive Property –2 sin2 – sin + 1 = 0 Simplify. 2 sin2 + sin – 1 = 0 Divide each side by –1. (2 sin – 1)(sin + 1) = 0 Factor. Example 1
Solve Equations for a Given Interval Now use the Zero Product Property. 2 sin – 1 = 0 sin + 1 = 0 2 sin = 1 sin = –1 = 270° = 30° or 150° Answer: Example 1
Solve Equations for a Given Interval Now use the Zero Product Property. 2 sin – 1 = 0 sin + 1 = 0 2 sin = 1 sin = –1 = 270° = 30° or 150° Answer: Since 0°≤ ≤ 180°, the solutions are 30°, and 150°. Example 1
A. Solve cos + = sin2for all values of if is measured in degrees. Look at the graph of y = cos – sin2 to find solutions of cos – sin2 = – Infinitely Many Solutions Example 2
Infinitely Many Solutions The solutions are 60°, 300°, and so on, and –60°, –300°, and so on. The period of the function is 360°. So the solutions can be written as 60° + k ● 360° and 300° + k ● 360°, where k is measured in degrees. Answer: Example 2
Infinitely Many Solutions The solutions are 60°, 300°, and so on, and –60°, –300°, and so on. The period of the function is 360°. So the solutions can be written as 60° + k ● 360° and 300° + k ● 360°, where k is measured in degrees. Answer: 60° + k ● 360° and 300° + k ● 360°, where k is measured in degrees. Example 2
Infinitely Many Solutions B. Solve 2cos = –1 for all values of if is measured in radians. 2cos = –1 Example 2
A. Solve cos 2 sin + 1 = 0 for all values of if is measured in degrees. A.0° + k● 360° and 45° + k ● 360° where k is any integer B.45° + k● 360° where k is any integer C.0° + k● 360° and 90° + k ● 360° where k is any integer D.90° + k● 360° where k is any integer Example 2
A. Solve cos 2 sin + 1 = 0 for all values of if is measured in degrees. A.0° + k● 360° and 45° + k ● 360° where k is any integer B.45° + k● 360° where k is any integer C.0° + k● 360° and 90° + k ● 360° where k is any integer D.90° + k● 360° where k is any integer Example 2
A. B. C. D. B. Solve 2 sin = –2 for all values of if is measured in radians. Example 2
A. B. C. D. B. Solve 2 sin = –2 for all values of if is measured in radians. Example 2
AMUSEMENT PARKSWhen you ride a Ferris wheel that has a diameter of 40 meters and turns at a rate of 1.5 revolutions per minute, the height above the ground, in meters, of your seat after t minutes can be modeled by the equation h = 21 – 20 cos 3t. How long after the Ferris wheel starts will your seat first be meters above the ground? Solve Trigonometric Equations Example 3
Replace h with Solve Trigonometric Equations Original equation Subtract 21 from each side. Divide each side by –20. Take the Arccosine. Example 3
The Arccosine of Solve Trigonometric Equations Divide each side by 3. Answer: Example 3
The Arccosine of Answer: Solve Trigonometric Equations Divide each side by 3. Example 3
AMUSEMENT PARKS When you ride a Ferris wheel thathas a diameter of 40 meters and turns at a rate of 1.5 revolutions per minute, the height above the ground,in meters, of your seat after t minutes can be modeled by the equation h = 21 – 20 cos 3t. How long after theFerris wheel starts will your seat first be 11 meters above the ground? A. about 7 seconds B. about 10 seconds C. about 13 seconds D. about 16 seconds Example 3
AMUSEMENT PARKS When you ride a Ferris wheel thathas a diameter of 40 meters and turns at a rate of 1.5 revolutions per minute, the height above the ground,in meters, of your seat after t minutes can be modeled by the equation h = 21 – 20 cos 3t. How long after theFerris wheel starts will your seat first be 11 meters above the ground? A. about 7 seconds B. about 10 seconds C. about 13 seconds D. about 16 seconds Example 3
sin = cos Divide each side by cos Determine Whether a Solution Exists A. Solve the equation sin cos = cos2 if 0 ≤ ≤ 2. sin cos = cos2 Original equation sin cos – cos2 = 0 Subtract cos2 from each side. cos (sin – cos )= 0 Factor. cos = 0 or sin – cos = 0 Zero Product Property Example 4