x = x 2
Given that x 1 and x 2 are the real solutions to the equation above and that x 3 and x 4 are the complex ones, calculate x 1 + x 2 + ∣ x 3 ∣ + ∣ x 4 ∣
Notation: ∣ z ∣ means the magnitude of z where z ∈ C .
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It can be factored as
x = x 4
x ( x 3 − 1 ) = 0
Now, three roots are 0 , 1 , ω , ω 2 where ω = imaginary cube root of unity .
Now ∣ ω ∣ = ∣ ω 2 ∣ = 1
Therefore 0 + 1 + ∣ ω ∣ + ∣ ω 2 ∣ = 3
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x = x 2 x = x 4 x 4 − x = 0 x ( x 3 − 1 ) = 0 x = 0 or x 3 − 1 = 0
The first part has one solution, as stated. The second part has three solutions, all of which have a magnitude (or absolute value) of 1 . It is not necessary to calculate the actual solutions, as long as you can visualize the magnitude. Thus, we have one solution with a magnitude of 0 and three solutions with a magnitude of 1 . Thus, the sum of the magnitude of the solutions is 1 × 0 + 3 × 1 = 3 .