686 CHAPTER 7 Trigonometric Identities and Equations CONCEPT PREVIEWUse identities to correctly complete each sentence. 6. If tanu = 2.6, then tan1-u2 = . 7. If cos u = -0.65, then cos1-u2 = . 8. If tanu = 1.6, then cot u = . 9. If cos u = 0.8 and sinu = 0.6, then tan1-u2 = . 10. If sinu = 2 3, then -sin1-u2 = . Find sinu. See Example 1. 11. cos u = 3 4, u in quadrant I 12. cos u = 5 6, u in quadrant I 13. cot u = - 1 5, u in quadrant IV 14. cot u = - 1 3, u in quadrant IV 15. cos1-u2 = 25 5 , tanu 60 16. cos1-u2 = 23 6 , cot u 60 17. tanu = - 26 2 , cos u 70 18. tanu = - 27 2 , sec u 70 19. sec u = 11 4 , cot u 60 20. sec u = 7 2, tanu 60 21. csc u = - 9 4 22. csc u = - 8 5 23. Why is it unnecessary to give the quadrant of u in Exercises 21 and 22? 24. Concept Check What is WRONG with the statement of this problem? Findcos1-u2 if cos u = 3. Concept Check Find ƒ1-x2 to determine whether each function is even or odd. 25. ƒ1x2 = sinx x 26. ƒ1x2 = x cos x Concept Check Identify the basic trigonometric function graphed, and determine whether it is even or odd. 27. −4 4 11p 4 11p 4 − 28. −4 4 11p 4 11p 4 − 29. −4 4 11p 4 11p 4 − 30. −4 4 11p 4 11p 4 − Find the remaining five trigonometric functions of u. See Example 1. 31. sinu = 2 3, u in quadrant II 32. cos u = 1 5, u in quadrant I 33. tanu = - 1 4, u in quadrant IV 34. csc u = - 5 2, u in quadrant III 35. cot u = 4 3, sinu 70 36. sinu = - 4 5, cos u 60 37. sec u = 4 3, sinu 60 38. cos u = - 1 4, sinu 70
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