Use an addition or subtraction formula to find the exact value
1) cos(165 degree)
2) cos(-13π/12)
thanks
Trigonometry
2011-09-26 12:59 am
回答 (1)
2011-09-26 1:18 am
✔ 最佳答案
1)cos 165°= cos (120 + 45)°= cos 120° cos 45° - sin 120° sin 45°= (- 1/2) (√2 / 2) - (√3 / 2) (√2 / 2) = - (√2 + √6) / 42)cos (- 13π/12)= cos (13π/12)= cos (5π/6 + π/4)= cos (5π/6) cos (π/4) - sin (5π/6) sin (π/4) = (- √3 / 2) (√2 / 2) - (1/2) (√2 / 2)= - (√2 + √6) / 4
收錄日期: 2021-04-21 22:21:53
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110925000051KK00663