Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

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## #1 2007-08-05 13:19:13

tony123
Member
Registered: 2007-08-03
Posts: 189

### prove

Last edited by tony123 (2007-08-05 13:21:31)

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## #2 2007-08-07 11:49:53

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

### Re: prove

First you show that sin80° = sin40° + sin20°. I have set this as a separate exercise for you to do:
http://www.mathsisfun.com/forum/viewtop … 580#p76580

Last edited by JaneFairfax (2007-08-07 11:53:15)

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## #3 2007-08-07 12:55:26

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

### Re: prove

Reason #131 why I hate trig.

"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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## #4 2007-08-07 13:00:30

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: prove

Nice job there Jane.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #5 2007-08-07 14:55:06

George,Y
Member
Registered: 2006-03-12
Posts: 1,316

### Re: prove

You've been so patient Janefairfax.

X'(y-Xβ)=0

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## #6 2007-08-07 19:53:02

Identity
Member
Registered: 2007-04-18
Posts: 934

### Re: prove

Wow. That is amazing!

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