M2 math trigonometry
回答 (2)
2011-01-16 3:27 am
✔ 最佳答案
sinAsinB = (1/2) (cos(A-B) - cos(A+B))[1/(2sin170)]-2sin70 =[1-4sin70sin170]/(2sin170) =[1-2(cos100-cos240)]/(2sin170)=1/(2sin170)-cos100/sin170+cos240/sin170=1/(2sin170)+cos80/cos80+cos240/sin170=1+1/(2sin170)+cos240/sin170=1+1/(2sin170)-1/(2sin170)=1
2011-01-16 3:21 am
[1/(2sin170)]-2sin70
=[1/(2sin10)]-2cos20
=[cos10/(sin20)]-2cos20
=(cos10-sin40)/(sin20)
=(sin80-sin40)/(sin20)
=2sin60sin20/(sin20)
=2(root(3))/2
=root(3)
=[1/(2sin10)]-2cos20
=[cos10/(sin20)]-2cos20
=(cos10-sin40)/(sin20)
=(sin80-sin40)/(sin20)
=2sin60sin20/(sin20)
=2(root(3))/2
=root(3)
收錄日期: 2021-04-26 14:05:05
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110115000051KK01006