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

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## #1 2007-08-06 11:19:13

tony123
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### prove

Last edited by tony123 (2007-08-06 11:21:31)

## #2 2007-08-08 09:49:53

JaneFairfax
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### 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 (2007-08-08 09:53:15)

Q: Who wrote the novels Mrs Dalloway and To the Lighthouse?

## #3 2007-08-08 10:55:26

Ricky
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### 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..."

## #4 2007-08-08 11:00:30

MathsIsFun

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### Re: prove

Nice job there Jane.

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

## #5 2007-08-08 12:55:06

George,Y
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### Re: prove

You've been so patient Janefairfax.

X'(y-Xβ)=0

## #6 2007-08-08 17:53:02

Identity
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### Re: prove

Wow. That is amazing!