Bonus Problem #2

Algebra Level 1

x 2 x 2 = 1 \large x^{2x^2} = 1

How many integers of x x satisfy the equation above?

Note: 0 0 0^0 is undefined.


The answer is 2.

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13 solutions

Paul Ryan Longhas
May 15, 2015

Case 1: 2 x 2 = 0 2x^2 = 0

x = 0 \Rightarrow x = 0 but if x = 0 x 2 x 2 = 0 2 0 2 1 x = 0 \Rightarrow x^{2x^2} = 0^{2*0^2} \neq 1

Case 2: x = 1 x = 1

x 2 x 2 = 1 2 1 2 = 1 \Rightarrow x^{2x^2} = 1^{2*1^2} = 1

Case 3: x = 1 x = -1 for even exponent

x 2 x 2 = ( 1 ) 2 ( 1 ) 2 = 1 \Rightarrow x^{2x^2} = (-1)^{2*(-1)^2} = 1

So, they have two value.

Moderator note:

There's a simpler approach.

Hint : x 2 x 2 = ( x 2 ) x 2 x^{2x^2} = (x^2)^{x^2} .

Nice solution sir. But is there any way to prove that these are the only two solutions?

Sravanth C. - 6 years, 1 month ago

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u can check it out by drawing the graph of y = y= x 2 x 2 x^{2x^2} and y = y= 1 1 , they both intersect at two integer points 0 0 and 1 1

check it out over here

Soumya Dubey - 6 years, 1 month ago

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What about x = 1 x=-1

Pranjal Jain - 5 years, 10 months ago

Why doesn't the graph show negative values of x? (Just want to know)

Ahmad Sofiullah - 5 years, 10 months ago

It could be argued that there could be 3 values. -1, 1 and 0.

Here are some sources that suggest that there are some ways that 0^0 = 1

https://www.math.hmc.edu/funfacts/ffiles/10005.3-5.shtml http://mathforum.org/dr.math/faq/faq.0.to.0.power.html http://www.askamathematician.com/2010/12/q-what-does-00-zero-raised-to-the-zeroth-power-equal-why-do-mathematicians-and-high-school-teachers-disagree/

Norm Nolasco - 5 years, 10 months ago

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Officially, 0 0 0^0 is undefined.

Whitney Clark - 5 years, 10 months ago

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You're no fun. Didn't you read any of the links I provided?

Norm Nolasco - 5 years, 10 months ago

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@Norm Nolasco There is a reason for why the value of 0 0 0^{0} is undefined.

We know that x 0 = 1 x^{0} = 1 but we also know that is 0 x = 0 0^{x} = 0

From the above points we have two values for 0 0 0^{0} - 1 and 0. So the value of 0 0 0^{0} remains undefined.

PS : There might be more ways to prove 0 0 0^{0} is undefined.But this is the method that i know.

Athiyaman Nallathambi - 5 years, 10 months ago

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@Athiyaman Nallathambi Algebraically, perhaps it should be 1. Using the "official" definition, a x : = e l n x a^x:=e^{ln x} , but ln 0 is undefined.

Whitney Clark - 5 years, 6 months ago

@Athiyaman Nallathambi Yes, it "should" be 1, but the official ruling is that it isn't anything at all. In a way it makes little practical difference, anyway.

Whitney Clark - 5 years, 6 months ago

That's exactly what I thought, but then since it was deemed incorrect, I suggested 2 values, excluding 0^0 .

Taran Kota - 5 years, 10 months ago

Why only 1, -1

aman Vijaywargi - 5 years, 10 months ago

Note x 2 x 2 = ( x 2 ) x 2 = 1 1 x^{2x^2}=(x^2)^{x^2}=1^1 so x 2 = 1 x = ± 1. x^2=1 \Rightarrow x= \pm 1.

Arian Tashakkor
May 15, 2015

Sravanth Chebrolu Proof that the cases are the few ones mentioned in the solution:

Let 0 < a 1 0<a \not = 1 be another answer (by false assumption).Then we'd have:

a 2 a 2 = 1 ( 2 a 2 ) l o g a = l o g 1 ( 2 a 2 ) l o g a = 0 a^{2a^2}=1 \rightarrow (2a^2) log \space {a} = log \space 1 \rightarrow (2a^2) log\space {a} = 0

2 a 2 = 0 l o g a = 0 a = 0 a = 1 \rightarrow 2a^2=0 \lor log \space{a}=0 \rightarrow a=0 \lor a=1

Which is indeed a contradiction that proves that a 0 a = 0 a = 1 \forall a \ge 0 \leftrightarrow a=0 \lor a=1

Also for x < 1 x < -1 we'll prove that the equation cannot hold:

x < 1 x 2 > 1 ( x 2 ) x 2 > 1 x 2 = 1 x 2 x 2 > 1 x < -1 \rightarrow x^2 > 1 \rightarrow (x^2)^{x^2} > 1^{x^2} = 1 \rightarrow x^{2x^2} > 1

And hence we're done.

By the way,how are you feeling?Are thing starting to get better?

Well done sir! and yes I'm a lot better now, but it's my father who is still down . . .

Sravanth C. - 6 years, 1 month ago

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Hope he gets better soon.And please don't call me sir xD, we merely have 2 years in difference!. Call me Arian if you wish.

Arian Tashakkor - 6 years, 1 month ago

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Thanks Arian! I hope what you hope too . . .

Sravanth C. - 6 years, 1 month ago
Christopher Unrau
Nov 27, 2015

Well if x 2 x 2 = 1 i f x = 1 , 1 2 = 1 { x }^{ 2x^{2} }=1\quad if\quad x=1,\quad { 1 }^{ 2 }=1 Considering the exponent is two multiplied by a number, and the answer is one, we can assume that the exponent cannot be higher than one. However, we can still test for negative one. x 2 x 2 = 1 , i f x = ( 1 ) , x 2 x 2 = 1 2 = 1 { x }^{ 2x^{ 2 } }=1,\quad if\quad x=(-1),\quad { x }^{ 2x^{ 2 } }={ -1 }^{ 2 }=1

Sara Flint
Mar 13, 2016

0^0 is not undefined. It is 1. The "correct" answer is two, with x being equal to either 0 or 1, but there could also be three solutions, with x being equal to -1.

Phillip Tago
Dec 3, 2015

Similarly we can just simplify it to

x^{2x^{2}} - 1 = 0

And just following through with that and expanding, we have

(x^{x^{2}} + 1) (x^{x^{2}} - 1)

Giving 2 solutions of 1, -1

(xᵡ² + 1)(xᵡ² ̶ 1) = 0 .... maybe that's enough... I hope.

Ben Habeahan
Aug 18, 2015

x 2 x 2 = ( x 2 ) x 2 = 1 = 1 1 x^{2x^2} = (x^2) ^ {x^2} =1={1}^{1} \\ so x 2 = 1 x = 1 , o r x = 1 \\ x^2=1 \\ x= 1,\ or\ x=-1 \\ So, they have t w o \boxed{two} value

1 and -1 because (-1)^2(-1)^2=1 and also anything power 1 is 1 itself.

Leandro Oliveira
Aug 10, 2015

Note that if $|x|>1$ , $x^2>1$ and this way, $(x^2)^{x^2}>1$. So, $|x|=1$ because $x$ is a integer number.

Case 1: 1^2*1²=1

Case 2: -1^2*(-1)²=1

0^0 is undefined.

Towhidd Towhidd
Jul 25, 2015

x^(2x^2)=1 or, log(x^(2x^2))=log1 or, (2x^2)logx=0 [as, log1=0] eighther, (2x^2)=0 or, logx=0 or, x=0 or x=1 that means x has two values

Alisa Meier
Jul 25, 2015

There are in fact 2 solutions:

-1,1 are all integers and solve the equation as one can easily verify.

Note: 0 0 0^0 is often considered indeterminate.

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