What To The What Is One?

Algebra Level 1

Find the number of real solutions of x x satisfying x x = 1 x^{x}=1 .

Note: 0 0 0^{0} is not defined.


The answer is 1.

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1 solution

Yash Dev Lamba
Mar 3, 2016

Take l o g log both sides

x l o g x = l o g 1 = 0 xlogx=log1=0

either x = 0 x=0 o r or l o g x = 0 logx=0

x = 0 , 1 x=0,1 but x 0 x\neq 0 ( 0 0 0^{0} is not defined)

Therefore only one solution x = 1 x=1

This solution is incomplete because it doesn't handle negative x x . (Compare: x x 1 = 1 x^{x-1} = 1 has two real solutions, but only one is found with this solution.)

Ivan Koswara - 5 years, 3 months ago

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Ya I am quite aware of it , you can upload new solution so I can also learn something

Yash Dev Lamba - 5 years, 3 months ago

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Why don't you post the solution or at least give some hints to solve your posted problem "spicy 1"?I even posted a report asking help but you do not reply?

Manish Maharaj - 5 years, 3 months ago

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@Manish Maharaj be calm I will upload soon

Yash Dev Lamba - 5 years, 3 months ago

The question does not state that x is real number, there are infinitely many solution when x is complex number...

Jack Tang - 5 years, 3 months ago

Interestingly, the solution is also consistent with the theorem which states that number of roots of the polynomial equation p ( x ) = 0 p(x) = 0 is equal to the degree of p ( x ) p(x) .

Harsh Khatri - 5 years, 3 months ago

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How so? x x x^x is not a polynomial.

Calvin Lin Staff - 5 years, 3 months ago

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Yes, it isn't.

What I meant was that we take the specific case of polynomials, i.e., when x takes only positive integral values.

The polynomial x n 1 = 0 x^n-1=0 is of degree n n and has n n roots. When n = 1 n=1 , x 1 1 = 0 x^1-1=0 has only one solution which is x = 1 x=1 .

So, the number of solutions is equal to the solution only when x = 1 x=1 .

It was just an observation that I stumbled upon.

Harsh Khatri - 5 years, 3 months ago

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@Harsh Khatri Polynomials \neq when x take only positive integer values. Please review the definition of Polynomials .

This is a bad way of thinking / interpreting the problem. Please do not do so. In fact, it is an "observation" that I want to warn against, because it screws with your understanding of the actual theory.

Calvin Lin Staff - 5 years, 3 months ago

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@Calvin Lin Ohh. Will take care not to jumble up concepts again and try to stick to the definitions.

That was really helpful. Thank you.

Harsh Khatri - 5 years, 3 months ago

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@Harsh Khatri Bonus: Is sin x \sin x a polynomial?

Nihar Mahajan - 5 years, 3 months ago

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@Nihar Mahajan in fact sin(x) can be approximated by power series

Vikas Srivastava - 5 years, 3 months ago

@Nihar Mahajan no at all sinx is not a polynomial

Yash Dev Lamba - 5 years, 3 months ago

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