Lots of 2019

Algebra Level 3

x 2019 + 2019 x + 2019 = 0 \large x^{2019} + 2019x + 2019 = 0

The sum of the 2019th powers of all the roots (real and complex) of the equation above can be expressed as a b c d - a^b c^d , where a a and c c are prime numbers.

Find a + b + c + d a + b + c + d .


The answer is 680.

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1 solution

Let the roots of the equation be a k a_k , where k = 1 , 2 , 3 , 2019 k=1, 2, 3, \dots 2019 . Then a k 2019 + 2019 a k + 2019 = 0 a_k^{2019} + 2019a_k + 2019 = 0 . Now we have:

k = 1 2019 a k 2019 = k = 1 2019 ( 2019 a k 2019 ) = 2019 k = 1 2019 a k k = 1 2019 2019 By Vieta’s formula = 2019 × 0 201 9 2 Since 2019 = 3 × 673 , = 3 2 × 67 3 2 where 3 and 673 are primes \begin{aligned} \sum_{k=1}^{2019}a_k^{2019} & = \sum_{k=1}^{2019} \left(-2019a_k - 2019\right) \\ & = - 2019 {\color{#3D99F6}\sum_{k=1}^{2019} a_k} - \sum_{k=1}^{2019} 2019 & \small \color{#3D99F6} \text{By Vieta's formula} \\ & = - 2019 \times {\color{#3D99F6}0} - 2019^2 & \small \color{#3D99F6} \text{Since }2019 = 3\times 673, \\ & = - 3^2 \times 673^2 & \small \color{#3D99F6} \text{where 3 and 673 are primes} \end{aligned}

Therefore, a + b + c + d = 3 + 2 + 673 + 2 = 680 a+b+c+d = 3+2+673+2 = \boxed{680} .


Reference: Vieta's formula

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