Exponents

Algebra Level 1

Find the value of x > 1 x>1 which satisfies the equation

x + x = x x . \large x + x = x^x.


The answer is 2.

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7 solutions

Amogh Keni
Dec 8, 2015

Here,

x+x= x^x

Then,

2x= x^x

Or,

x^x= 2x

x^(x-1)= 2^1

i.e. x^(x-1)= 2^(2-1)

Comparing we get,

x=2

And it's pretty to guess that x x is very small

Arulx Z - 5 years, 5 months ago

Brilliant and simpleeee!!!

Adarsh pankaj - 5 years, 5 months ago
Benjamin Segall
Dec 23, 2015

x + x = x x l o g ( x ) + l o g ( x ) = l o g ( x x ) 2 × l o g ( x ) = l o g ( x x ) 2 × l o g ( x ) = x × l o g ( x ) 2 × l o g ( x ) l o g ( x ) = x 2 = x x + x = x^{x} \\ log(x)+log(x)=log(x^{x})\\ 2 \times log(x)=log(x^{x}) \\ 2 \times log(x)=x \times log(x) \\ \frac{2 \times log(x)}{log(x)}=x \\ 2 = x

This is incorrect. Taking the log of both sides, you cannot split log(x+x) = log(x)+log(x)

Shageenth Sandrakumar - 5 years, 2 months ago
Márcio Gomes
Dec 21, 2015

If we rewrite that expression in x + x = 2 x x + x = 2x , we have to satisfy the equation x x = 2 x x^x = 2x . By definition, a exponential must have the following form: x x = x x x x x . . . x^x = xxxxx... , with all terms with the same value. So, with the condition x > 1 x > 1 , the value of x x must be equal to 2.

Rimpy Jha
Nov 26, 2015

In this question, we have to use some trial and error method tricks. If we use some logic, we can certifying that number must be either 1or 2 because of they are the only options. Then by he equation we have to suggest the right answer.

Evan Huynh
Dec 21, 2015

2 is a very special number

Rutaskom Namhar
Dec 21, 2015

If x is a real numbr , the answer is 2 . But if x is not a real numbr , the answer is 0..

0 is a real number and isn't a solution. because 0 0 0^0 isn't a real number

Pablo Cesar Herrera Ortiz - 5 years, 5 months ago

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Actually, X = 0 it is not a solution because does not satisfy X < 0 nor x^x = x + x

José Luis Gallegos Cárdenas - 5 years, 5 months ago

Wrong. 0 0 = 1 0^0 = 1 , and 1 is a real number. Because all real numbers to the zero power is by definition equal to 1. Therefore, isn't a solution for this problem.

Márcio Gomes - 5 years, 5 months ago

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0^0 is undefined. The rule is a^0 =1 for all real a not equal to 0.

Julian Fuller - 5 years, 5 months ago

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@Julian Fuller Please, read these links: Link 1 Link 2

Márcio Gomes - 5 years, 5 months ago

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@Márcio Gomes About those links you showed. Have a subtle conceptual mistakes. It's very interesting find them

Pablo Cesar Herrera Ortiz - 5 years, 5 months ago

That's completely wrong if you supose 0 0 0^0 is a real number you will get contradictions like 0 0 = 0 a a = 0 a 0 a = 0 0 = ? 0^0 = 0 ^{a-a}=\frac{0^a}{0^a}=\frac{0}{0}=?

Pablo Cesar Herrera Ortiz - 5 years, 5 months ago
Rishabh Jain
Dec 23, 2015

Here,

x+x= x^x

Then,

2x= x^x

Or,

x^x= 2x

x^(x-1)= 2^1

i.e. x^(x-1)= 2^(2-1)

Comparing we get,

x=2. RJ

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