e π or π e
Which of the above numbers is larger?
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since e^x > 1+x we can get a beter approximation posing x=π/e :
e^(π/e) > 1+ π/e leads to e^(e+π) > (e+π)^e
The first line is always true. The second line is true if x is positive. What if x is negative?
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It works with any x, even negative ones. It's a series taught in most Calculus 2 courses.
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Yes, that is true. But it is more difficult to conclude that the negative case is true, i.e. you can't just conclude it by the algebra given in the solution I referred to.
since pi is greater than e pi/e -l is positive
It would be e x ≥ 1 + x , as when x = 0 , it gives 1 at the left side and... 1 at the right one. Not that it affects your reasoning.
Elegant! I like it.
Consider a function f(x) = x x 1
Differentiating with respect to x,
f '(x) = x x 1 × [ x 2 1 − x 2 l n ( x ) ]
When f(x) is decreasing f '(x) < 0,
Since x x 1 & x 2 1 are greater than 0, it implies 1 − l n ( x ) < 0
l n ( x ) > 1
x > e
Hence, f(x) is decreasing in the region, x > e.
By definition of decreasing function as,
π > e
f ( π ) < f ( e )
π π 1 < e e 1
Raising to π × e on both sides,
π e < e π
Fantastic.
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Thanks, but it's just basic use of differentiation.
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Mohammed azad is actually right. Please explain how 1/(x^x) is positive?
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@Ananya Prakash – The function isn't defined on x < 0. And it is always greater than 0 for x > 0.
say something
How is it that 1/(x)^(x) is greater than 0?! To further assert my point: 1/(-1)^(-1) is -1 which is clearly less than 0. And something else The derivative for f(x) = 1/x^x is f'(x) = -x^(-x) * (1+ln(x))
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The function isn't defined for x < 0
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if I'm not mistaken, undefined means not solvable. in the instant example, it clearly was solved - and therefore is clearly defined.
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@Marc Brothers – @Marc Brothers ! For Better understanding
By undefined, I mean that the function doesn't have real values at those x. Eg : y = x is not defined for x <0. For the function I specified it is undefined is cause at all points between 2 negative integers ( − 1 ) s o m e t h i n g f r a c t i o n a l is not defined.
What about the derivative?! It's incorrect as I said. And what exactly did you prove near the end?! That 1/(pi^pi) < 1/(e^e) Well, one doesn't need to differentiate anything to come up with this result because 1/x^x is always smaller than 1/y^y if x > y for x, y >= 1 because a positive number greater than one raised to itself is always smaller than another number that is greater than it when raised to itself. The same with 2^2 < 3^3 and I fail to see how you used this finding to come with your final answer. And about your differentiation, the correct answer would be that For x>0, 1/x^x is decreasing as x>1/e, and since both pi and e are greater than 1/e, you didn't have any trouble proving that 1/pi^pi < 1/e^e which didn't need proving and I can't see how it led you to your final conclusion. To prove my point about the differentiatipn, you said that for x>0, the function is decreasing on x>e, then try 1/2^2 < 1/1^1 Here the function is decreasing for x less than e.
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@Mohamed Azab – The function isn't x x 1 , it is x x 1 , which are two completely different functions. So half of your comment doesn't make sense whatsoever. The differentiation I did is correct, you could check it out. Thus, the function is decreasing for x > e, which is exactly what I wrote.
Well, why would you go to the extra effort of using a differentiation for such a simple question? Both numbers are constants. Up to 20 decimal places, these are the answers I got:
pi^e=22.459157718361045464164280552768 e^pi=23.140692632779268996093438846063
e^pi is larger. That's it.
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I didn't want to use a calculator/ excel or any other aid.
e π π ln e e ln e So we look at the function f ( x ) which reaches the maxima at x 2 x 1 x − 1 ln x or, x Hence, e ln e e π ≤ = ≥ π e ≤ = ≥ e ln π ≤ = ≥ π ln π = x ln x = 0 = e ≥ π ln π ≥ π e
It is true that e^x> x^e if x doesn't equal e
I did it like, 3^4 is greater than 4^3 As π is greater than e, thus e^π > π^e xD
It doesn't have to be like that all the time. Take 2 and 3 as example. In general, all numbers larger than approximately 2.479 follow the rule: smaller^bigger>bigger^smaller. But that's not the point here, try using derivative and calculus :)
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Could you please expand where 2.479 come from? Are you analyzing f(x)=(x+e)^x -x^(x+e)?
e to the power of any real number other than e itself will be greater than the number to the power of e
Just look at the exponent; pi = 3.14 but Euler's = 2.71. Therefore, 2.71^3.14 > 3.14^2.71
3^2 or 2^3 doesn't apply to just look at the exponents
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What do you mean it doesn't apply? Pi and e are both constants. I solved it using both alternately as base and exponent up to 20 decimal places, just to make absolutely sure.
pi^e=22.459157718361045464164280552768 e^pi=23.140692632779268996093438846063
e^pi's obviously larger.
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Lance's solution was to simply look at the exponents and see which is larger. Gianpiero was just providing an example where the rule does not work to show why that isn't a valid way to solve. He wasn't denying that e^pi is the right answer.
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@Ryan Henderson – to further the point, actually got the question wrong by rounding to two and three.
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∵ e x = 1 + x + 2 ! x 2 + . . . ∴ e x > 1 + x . Substitute in x = e π − 1 , giving e e π − 1 > e π ⇒ e e π > π ⇒ e π > π e .