悠闲数学娱乐论坛(第3版)»论坛 › 数学区 › 初等数学讨论 › 三角恒等式

Return to list New

View 1199|Reply 3

三角恒等式

[Copy link]

462 Threads	969 Posts	9934 Credits

Credits: 9934

Send PM

青青子衿 Posted at 2014-1-31 18:31:13 |Read mode

求证：
\[\sum_{i=1}^n3^{i-1}\sin^3\frac{\theta}{3^i}=\frac{3^n\sin\frac{\theta}{3^n}-\sin\theta}{4}\]

Reply Edit

87 Threads	2383 Posts	110K Credits

Credits: 13325

Send PM

其妙 Posted at 2014-2-3 14:06:01

回复 1# 青青子衿
求导？

Reply Edit

22 Threads	69 Posts	525 Credits

Credits: 525

Send PM

wzxsjz Posted at 2014-2-3 18:27:55

Last edited by wzxsjz at 2014-2-3 18:50:00$sin3x=3sinx-4sin^3x$

Reply Edit

87 Threads	2383 Posts	110K Credits

Credits: 13325

Send PM

其妙 Posted at 2014-2-3 18:41:54

Last edited by 其妙 at 2014-2-3 20:56:00回复 4# wzxsjz
不错！$4\sin^3x=3\sin x-\sin3x$

Reply Edit

Return to list New

手机版Mobile version|Leisure Math Forum

2025-4-22 03:31 GMT+8

Powered by Discuz!

× Quick Reply To Top Return to the list