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# Hprec9 2

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### Hprec9 2

1. 1. 9-2: Addition and Subtraction Identities Learning Goals: •Use the addition and subtraction identities for sine, cosine & tangent ©2009 Roy L. Gover (www.mrgover.com)
2. 2. Review Find the exact values: 1. sin 2. cos180 2 3. sin 4. sin 270 3 5. cos 6. cos 2 2 ° ° π π π π
3. 3. Review 60° 30° 1 23 45° 45° 1 1 2
4. 4. Review 1 23 1 1 2 π 6 π 3 π 4 π 4
5. 5. Review Find the exact values: 1. sin 30 2. tan 6 3. cos 45 4. sin 3 5 5. cos 6. tan220 4 ° ° ° π π π
6. 6. Does cos 40°+ cos 10°=cos 50°? Analysis Inquiring Minds Want To Know…
7. 7. cos(α+β)=cosα cosβ-sinα sinβ cos(α-β)=cosα cosβ+sinα sinβ Addition & Subtraction Identities for Cosine: Important Idea cos( ) cos cos sin sin α β α β α β ± = m
8. 8. Example Find the exact value of cos 75° using the values of the function for 30° and 45°
9. 9. Example Find the exact value of cos using the values of the function for and π 3 π 4 7π 12    ÷  
10. 10. Try This Find the exact value of cos 15° using the values of the function for 60° and 45°. Hint: cos 15°=cos(60°-45°) 2 6 4 4 +
11. 11. Try This Find exact value of cos using the values of the function for and . Hint: cos = cos 2 6 4 4 + π 12    ÷   π 3 π 4π 12    ÷   π π 3 4   − ÷  
12. 12. Example Rewrite the given expression in terms of sin x and/or cos x: cos(x + )π
13. 13. sin(α+β)=sinα cosβ+cosα sinβ sin(α-β)=sinα cosβ - cosα sinβ Addition & Subtraction Identities for Sine: Important Idea sin( ) sin cos cos sin α β α β α β ± = ±
14. 14. Example Find the exact value of sin 75°. Simplify your answer.
15. 15. Example Find exact value of sin Hint: Simplify your answer. 13π 12    ÷  5π π 13π 4 6 12   − = ÷  
16. 16. Try This Find exact value of sin Hint: 5π 12    ÷  2π π 5π 3 4 12   − = ÷   Simplify your answer. 6 2 4 +
17. 17. Try This Verify the identity: sin(270°+x)=-cos x
18. 18. Solution sin(270 ) sin 270 cos cos270 sin 1(cos ) 0(sin ) cos x x x x x x °+ = ° + ° = − + = −
19. 19. tan tan tan( ) 1 tan tan α β α β α β + + = − tan tan tan( ) 1 tan tan α β α β α β − − = + Addition & Subtraction Identities for Tangent… Important Idea
20. 20. tan tan tan( ) 1 tan tan α β α β α β ± ± = m Addition & Subtraction Identities for Tangent-the condensed form: Important Idea
21. 21. Example Find the exact value of tan 15° using the values of the tan function for 45° and 30°. Simplify your answer.
22. 22. Try This If sin A= & cos B= , find tan(A+B). 4 5 3 5 24 7 −
23. 23. Lesson Close Describe a method for finding the exact value of sin 105°.
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