Irrational^rational = rational

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  • #1
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Is it true that in some cases an irrational number raised to a rational power is rational? If so what kinds of irrational numbers?
 

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  • #2
jgens
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Yes. For your first question note that √22 = 2. For your second question all number of this form should be algebraic.

Edit: As Mark44 pointed out below I need to add the caveat that the exponent be non-zero for my second claim to hold.
 
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  • #3
pwsnafu
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It's also worth pointing out that irrational to the irrational can be rational.

The Gelfond-Schneider theorem says: if ##a## and ##b## are algebraic, with ##a \neq 1,0## and ##b## irrational, then ##a^b## is transcendental.

This means that ##\sqrt{2}^{\sqrt{2}}## is transcendental (hence irrational). Raise this to the power of ##\sqrt{2}## and you get 2.
 
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  • #4
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Is it true that in some cases an irrational number raised to a rational power is rational? If so what kinds of irrational numbers?
A very simple example is ##\pi^0 = 1##.
##\pi## is irrational, and 0 is rational.
 
  • #5
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if the order of the root is say x, and the power you raise are multiples of x , then it becomes a rational number(or if the power is 0)
example:√2^4=4
 
  • #6
HallsofIvy
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Note that the irrational number has to be algebraic. A transcendental number raised to a rational power cannot be rational. In fact, it must still be transcendental.
 
  • #7
DrClaude
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Note that the irrational number has to be algebraic. A transcendental number raised to a rational power cannot be rational. In fact, it must still be transcendental.
A very simple example is ##\pi^0 = 1##.
##\pi## is irrational, and 0 is rational.
Isn't there a contradiction here?
 
  • #8
arildno
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Isn't there a contradiction here?
I think you just became a candidate for the Fields medal! :smile:
 
  • #9
DrClaude
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I think you just became a candidate for the Fields medal! :smile:
No , I just became the candidate for another coffee!

Sorry Mark44, completely missed your humor there...
 
  • #10
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No , I just became the candidate for another coffee!

Sorry Mark44, completely missed your humor there...
That was arildno...
 
  • #11
DrClaude
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That was arildno...
I thought you were trying to be funny by proposing the trivial case "to the power of 0". :redface:
 

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