情趣生活

情趣生活 => 灵机一动 => Topic started by: MrPuzzle on 七月 29, 2004, 09:47:05 am

Title: Advanced Trigonometry :)
Post by: MrPuzzle on 七月 29, 2004, 09:47:05 am
Prove

  cos π/7 - cos 2π/7 + cos 3π/7 = 1/2

without actually computing the values.
Title: Advanced Trigonometry :)
Post by: idiot94 on 七月 29, 2004, 04:00:15 pm
Consider the roots of x^7 = 1, you immediately got the result.

Friends, I will be on my way to Alaska tomorrow morning! :) ... (that is why I was busy this week... to finish up the stuff at work before vacation.. ~_* )...

Hope I can bring some cool pics back for you guys :)
Title: Advanced Trigonometry :)
Post by: MrPuzzle on 七月 30, 2004, 09:06:32 am
Yes, X^7=1 is the key.

Good job and have a wonderful vacation.