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#1 2008-05-11 15:05:58
- SvenBee
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Yay for a wacky proof!
All right 10 points to whomever finds the fallacy in this proof 
e...the red-headed stepchild of math.
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#2 2008-05-11 18:29:25
- luca-deltodesco
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Re: Yay for a wacky proof!
since your taking the square root, you need ±
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#3 2008-05-12 01:15:40
- SvenBee
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Re: Yay for a wacky proof!
So close but not quite on target, 5 points.
e...the red-headed stepchild of math.
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#4 2008-05-12 03:08:03
- Daniel123
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Re: Yay for a wacky proof!
Since we know that cos x is positive when
, and negative when .Offline
#5 2008-05-12 03:09:09
- Dragonshade
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Re: Yay for a wacky proof!
I guess its more like
The trick of this is that, he changed the domain and range
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#6 2008-05-12 03:17:55
- SvenBee
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Re: Yay for a wacky proof!
That's correct, but the more obvious fallacy lies in the property:
This property holds true for fractional exponents as well, but only when a is positive, which is not the case for the trig function.
e...the red-headed stepchild of math.
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#7 2008-05-12 03:23:18
- Daniel123
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Re: Yay for a wacky proof!
That's correct, but the more obvious fallacy lies in the property:
This property holds true for fractional exponents as well, but only when a is positive, which is not the case for the trig function.
It will hold for negative a if the denominator of the fractional exponent (bc) is odd (although in this case it isn't).
Last edited by Daniel123 (2008-05-12 03:27:34)
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#8 2008-05-12 03:30:37
- SvenBee
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Re: Yay for a wacky proof!
Yes but whether or not the "a" is negative or positive must be established before applying the property and that's not the case here because the property is applied before pi is substituted in.
e...the red-headed stepchild of math.
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