Algebra

Level 1

Given that x + 1 x = 0 x+\dfrac{1}{x}=0 , find x 16 + 1 x 16 x^{16}+\dfrac{1}{x^{16}} .

Details and Assumptions: x x need not be a real number.


The answer is 2.

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3 solutions

Finn Hulse
Apr 19, 2014

First off, rearrange the given equation. This is simply x = 1 x x=\frac{-1}{x} . Multiplying both sides by x x , x 2 = 1 x^2=-1 , and thus x = ± i x=\pm i . Now let us evaluate x 16 x^{16} . Remember, i n = i n ( m o d 4 ) i^n=i^{n \pmod{4}} . Thus, i 16 = i 0 = 1 i^{16}=i^0=1 . Now, plugging this newfound value of x 16 x^{16} into the desired equation, we find 1 + 1 = 2 1+1=\boxed{2} . Great problem @Victor Loh !

good problem

Prajwal Kavad - 7 years, 1 month ago

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Yeah. :D

Finn Hulse - 7 years, 1 month ago

x + 1 x = 0 x + \dfrac{1}{x} = 0

x 2 + 1 x = 0 \dfrac{x^2 +1}{x} = 0

x 2 + 1 = 0 x^2 + 1 = 0 (Since x 0 x \not = 0 )

x 2 = 1 x^2 = -1

x = ± i x = \pm i

Putting the value of x in x 16 + 1 x 16 x^{16} + \dfrac{1}{x^{16}} , we get,

( ± i ) 16 + 1 ( ± i ) 16 (\pm i)^{16} + \dfrac{1}{(\pm i)^{16}}

= ( 1 ) 8 + 1 ( 1 ) 8 = (-1)^8 + \dfrac{1}{(-1)^8}

= 1 + 1 1 = 1 + \dfrac{1}{1}

= 2 = \boxed{2}

. .
Feb 17, 2021

We know that zero can't be a denominator, so let's solve the equation.

First, x + 1 x = 0 x 2 + 1 = 0 x 2 = 1 x = ± i x + \frac { 1 } { x } = 0 \rightarrow x^{2} + 1 = 0 \rightarrow x^{2} = -1 \Rightarrow x = \pm i .

So, the roots for the equation are ± i \pm i .

Then, let's find the value of x 16 + 1 x 16 x^{16} + \frac { 1 } { x ^ { 16 } } .

Substituting x = ± i x = \pm i to the equation, we get ( ± i ) 16 + 1 ( ± i ) 16 ( \pm i ) ^ { 16 } + \frac { 1 } { ( \pm i ) ^ { 16 } } .

Then, we get 1 + 1 1 + 1 .

Thus, the value is 2 \boxed { 2 } .

2 \therefore \boxed { 2 } is the answer for the problem.

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