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#1 2006-03-09 19:45:03
- amonjezi
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- Registered: 2006-03-09
- Posts: 9
solve sin(36)
hi!
please solve this problem!
sin(36)?
without calculator!
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#2 2006-03-09 20:18:13
- krassi_holmz
- Real Member
- Registered: 2005-12-02
- Posts: 1,905
Re: solve sin(36)
IPBLE: Increasing Performance By Lowering Expectations.
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#3 2006-03-09 23:03:57
- MathsIsFun
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- Registered: 2005-01-21
- Posts: 7,713
Re: solve sin(36)
Seems to be right!
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
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#4 2006-03-09 23:18:42
- krassi_holmz
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- Registered: 2005-12-02
- Posts: 1,905
Re: solve sin(36)
Is 36 degrees or 36 rad?
If it's 36 radians, we get:
IPBLE: Increasing Performance By Lowering Expectations.
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#5 2006-03-11 01:44:13
- amonjezi
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- Registered: 2006-03-09
- Posts: 9
Re: solve sin(36)
hi krassi
degrees no radians
thank u
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#6 2006-03-13 03:49:39
- George,Y
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- Registered: 2006-03-12
- Posts: 1,379
Re: solve sin(36)
thiat used to be one of my high school excercise.
sin36 = 2 sin18 cos18 = 2 cos72 sin72
2 (sin36)^2=8 (cos72)^2 [1- (cos72)^2]
1 - cos72=8 (cos72)^2 [1- (cos72)^2]
cos72=sin18=x
1-x=8 x^2 (1 - x^2) = 8 x^2 (1-x)(1+x) = (1-x)(8 x^2+8 x^3)
x<1, so 8 x^3+8 x^2-1=0
solve it and get sin18, further get cos18, sin36 = 2 sin18 cos18
X'(y-Xβ)=0
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