Can anyone solve this question?
Find the value of cos10-sin80. Evaluate the value of (cos10+cos20+....+cos80)-(sin10+sin20+.....+sin80). Briefly explain how you get the answer.
中三數學題一問
2010-08-18 3:26 am
回答 (2)
2010-08-18 3:33 am
✔ 最佳答案
cos10 - sin80= sin(90 - 10) - sin80
= 0
Similiar , cosx - sin(90 - x) = 0 , so
(cos10 + cos20 + ... + cos80) - (sin10 + sin20 + ... + sin80)
= (cos10 - sin80) + (cos20 - sin70) + (cos30 - sin60) + (cos40 - cos50) + (cos50 - sin40) + (cos60 - sin30) + (cos70 - sin20) + (cos80 - sin10)
= 0 + 0 + 0 + ... + 0
= 0
2010-08-18 3:31 am
cos10 - sin80 = sin(90 - 10) - sin80 = sin80 - sin80 = 0
since cos10 = sin80,
(cos10+cos20+....+cos80)-(sin10+sin20+.....+sin80)
= sin80 + sin70 + sin60 + ........ + sin10 - (sin10 + sin20 + ... + sin80)
= 0
MMK
since cos10 = sin80,
(cos10+cos20+....+cos80)-(sin10+sin20+.....+sin80)
= sin80 + sin70 + sin60 + ........ + sin10 - (sin10 + sin20 + ... + sin80)
= 0
MMK
收錄日期: 2021-04-21 22:13:08
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100817000051KK01544