F4 maths 基本三角學
回答 (3)
2013-10-01 2:52 am
✔ 最佳答案
sin^2 10°+sin^2 20°+sin^2 30°+...+sin^2 80°=sin^2 10°+sin^2 80°+sin^2 20°+sin^2 70°+sin^2 30°+sin^2 60°+sin^2 40°+sin^2 50°
=sin^2 10°+cos^2 10°+sin^2 20°+cos^2 20°+sin^2 30°+cos^2 30°+sin^2 40°+cos^2 40°
=1+1+1+1
=4
參考: me
2013-10-01 12:27 pm
首先, sin^2 &+cos^ &=1 &是角度
sin&=cos(90°-&)
sin^2 10°+sin^2 20°+sin^2 30°+...+sin^2 80°
=sin^2 10°+sin^2 20°+sin^2 30°+sin^2 40°+cos^2 40°+cos^2 30°+cos^2 20°
+cos^2 10°
=(sin^2 10°+cos^2 10°)+(sin^2 20°+cos^2 20°)+(sin^2 30°+cos^2 30°)+(sin^2 40°+cos^2 40°)
=1+1+1+1
2013-10-01 04:27:32 補充：
=4
sin&=cos(90°-&)
sin^2 10°+sin^2 20°+sin^2 30°+...+sin^2 80°
=sin^2 10°+sin^2 20°+sin^2 30°+sin^2 40°+cos^2 40°+cos^2 30°+cos^2 20°
+cos^2 10°
=(sin^2 10°+cos^2 10°)+(sin^2 20°+cos^2 20°)+(sin^2 30°+cos^2 30°)+(sin^2 40°+cos^2 40°)
=1+1+1+1
2013-10-01 04:27:32 補充：
=4
2013-10-01 2:54 am
sin^2 10°+sin^2 20°+sin^2 30°+...+sin^2 80°
= sin^2 10°+sin^2 20°+sin^2 30°+sin^2 40°+cos^2 40°+cos^2 30°+cos^2 20°+cos^2 10°
= (sin^2 10°+cos^2 10°)+(sin^2 20°+cos^2 20°)+(sin^2 30°+cos^2 30°)+(sin^2 40°+cos^2 40°)
= 4
= sin^2 10°+sin^2 20°+sin^2 30°+sin^2 40°+cos^2 40°+cos^2 30°+cos^2 20°+cos^2 10°
= (sin^2 10°+cos^2 10°)+(sin^2 20°+cos^2 20°)+(sin^2 30°+cos^2 30°)+(sin^2 40°+cos^2 40°)
= 4
收錄日期: 2021-04-20 14:22:07
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20130930000051KK00171