Inspired by Paul Ryan Longhas

Algebra Level 2

How many complex solutions are there to the equation below?

x 2 + x x = 1 x^2 + \frac{x}{x} = 1


Inspiration

Infinitely many 1 None 2

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5 solutions

Pranshu Gaba
Feb 7, 2015

x x cannot be 0 0 , otherwise the LHS will be undefined.

Since x 0 x\neq 0 , x x = 1 \dfrac{x}{x} = 1 . The equation becomes x 2 + 1 = 1 x^2+1=1

x 2 = 0 \implies x^2=0

x = 0 \implies x=0 . However x x cannot be 0 0 , therefore there are no complex solutions.

Lol. I should have had faith in my intuition.

Oyekola Oyekole - 6 years, 4 months ago

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This question was intentionally tricky. Click through on the inspiration, which deals with a similar scenario, though not in such an obvious manner.

Calvin Lin Staff - 6 years, 4 months ago

These arguments are false. 0/0 is permitted as an indeterminate form. One must look to the limiting case as x tends to 0. In this case l'Hopital's rule applies and one may write lim {x\to 0}(x/x)=lim {x\to 0}(1/1)=1. Sorry guys but you're wrong. There is one solution and its zero (twice, degenerately).

Douglas Mclean - 5 years, 4 months ago

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Absolutely right.

Ber Gui - 5 years ago

we don't divide i by itself to get 1?

Jorge Alonso - 6 years, 4 months ago

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Note that i 2 + i i = 1 + 1 = 0 1 i^ 2 + \frac{ i } { i } = -1 + 1 = 0 \neq 1 .

So yes, when we divide i i by itself we get 1. However, i i is not a solution to the equation.

Calvin Lin Staff - 6 years, 4 months ago

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oh yeah, my bad. thanks

Jorge Alonso - 6 years, 3 months ago

I didn't notice COMPLEX SOLUTION.

niloy debnath - 5 years ago

I don't follow the logic here. Why is it that because x = 0, there are no complex solutions? I figured because x cannot be zero and it's quadratic, that there'd still need to be 2 solutions, and since 0 can't be one of those, it led me to believe that there must be some imaginary roots?

Although, if you calculate the discriminant, you end up with 0, which implies a multiplicity of 2 for x = 0, but that still can't be the solution... any insight appreciated.

Oli Hohman - 6 years, 4 months ago

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Note that the question asks for "how many complex solutions" , and not "what are the complex solutions". This is why the answer is "none", instead of "0".

It cannot be 0 because you cannot divide by 0. In particular, 0 0 \frac{ 0}{0} is undefined, and is not equal to 1.

If you went to multiply throughout by x x , you will obtain the equation x 2 = 0 x^2 = 0 . It has a repeated root (like you mentioned) of 0, which is not a valid answer.

Calvin Lin Staff - 6 years, 4 months ago

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As the question asked "how many complex solutions" the function should be f(z)=z^2+(z/z) which has a removable singularity at z=0 , when removed gives f(0)=1 so actually there is a solution :-s

Ross Creed - 5 years, 4 months ago

what if x is infinitely small no!! then its correct. So it should be specified that only integers, else the question is wrong

Arjun SivaÞrasadam - 5 years, 2 months ago

that's interesting. I guess we don't divide i by itself to get i because i/i = sqrt(-1/-1)=sqr(-1) which is not real, and 1 is real

Jorge Alonso - 6 years, 4 months ago

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minus divided by a minus is a positive ?

John Wyatt - 5 years, 8 months ago

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yeah because 1=-1 (-1)=-1 (1/-1)=-1*1/-1=-1/-1

Jorge Alonso - 5 years, 4 months ago
Patrick Engelmann
Feb 12, 2015

x 2 + x x = 1 x^{2} + \frac{x}{x} = 1

We can see that the only restriction is that x 0 x\ne0 , because then we'd divide by 0, which is undefined. If we assume this, we can do the following steps without any problems.

x 2 + x x = 1 x^{2} + \frac{x}{x} = 1

x ( x + 1 x ) = 1 \Longleftrightarrow x ( x + \frac{1}{x} ) = 1

x + 1 x = 1 x \Longleftrightarrow x + \frac{1}{x} = \frac{1}{x}

x = 0 \Longleftrightarrow x = 0

From the last statement we get the information that the equation x 2 + x x = 1 x^{2} + \frac{x}{x} = 1 can only be true, if and only if x = 0 x = 0 . This is a contradiction to our restriction for x 0 x\ne0 . Thus, there are no complex solutions to this equation.

Yay! Congrats!

Calvin Lin Staff - 6 years, 4 months ago
Kranthi Kumar
Feb 13, 2015

since x/x = 1

x²+1=1

x²=0

x=0 but x can't be 0......bcoz if x=0 x/x would become undefined.

Therefore, no solution.

Great job!

Calvin Lin Staff - 6 years, 3 months ago

x/x = 1 So we get: x^2 + 1 = 1 x^2 =1-1 x^2 = 0 Since x can never be 0. There would be no Solution

Good job :)

Calvin Lin Staff - 6 years, 3 months ago
Viki Zeta
Sep 5, 2016

x 2 + x x = 1 x 3 + x x = 1 x 3 + x = x x 3 = 0 x = 0. or, x 2 + x x = 1 x 2 + 1 = 1 x 2 = 0 x = 0 So, it has only one real solution ‘0’ and no complex solution. x^2 + \dfrac{x}{x} = 1\\ \dfrac{x^3 + x}{x} = 1 \\ x^3 + x = x \\ x^3 = 0 \\ x = 0.\\ \text{or,} \\ x^2 + \dfrac{x}{x} = 1 \\ x^2 + 1 = 1\\ x^2 = 0\\ x = 0 \\ \text{So, it has only one real solution `0' and no complex solution.}

I was thinking x= +/- ((sqrt 2) - 1)

Scott Leonard - 4 years, 7 months ago

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