One variable equation

Algebra Level 3

a + 56 + a 2 2018 + 56 + a + 5 6 2 2018 = 44051 2018 \large \frac{a+56+a^2}{2018} + \frac{56+a+56^2}{2018} = \frac{44051}{2018}

Find the minimum value of 2018 + a 2018 + a .


The answer is 1815.

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1 solution

Victor Dumbrava
Feb 4, 2018

It all comes down to a quadratic equation: a + 56 + a 2 2018 + 56 + a + 5 6 2 2018 = 44051 2018 \frac{a+56+a^2}{2018} + \frac{56+a+56^2}{2018} = \frac{44051}{2018} Multiply both sides by 2018 2018 : a 2 + 2 a + 3248 = 44051 a^2+2a+3248=44051 Subtracting 44051 44051 from both sides: a 2 + 2 a 40803 = 0 a^2+2a-40803=0 The coefficients are as follows: x = 1 , y = 2 , z = 40803 x=1,\space y=2,\space z=-40803 . Now writing the quadratic equation: a 12 = y ± Δ 2 x a_{12}=\frac{-y\pm\sqrt{\Delta}}{2x} Whereas Δ \Delta is the discriminant, Δ = y 2 4 x z \Delta=y^2-4xz . Δ = 2 2 + 4 40803 = 4 40804 \Delta=2^2+4\cdot 40803=4\cdot 40804 Now, substituting with the numerical values: a 12 = 2 ± 4 40804 2 a_{12}=\frac{-2\pm\sqrt{4\cdot 40804}}{2} A nice observation to make our life easier: 40804 = 20 2 2 40804=202^2 : a 12 = 2 ± 2 202 2 = 1 ± 202 a_{12}=\frac{-2\pm 2\cdot 202}{2} = -1\pm 202 So a a is either 201 201 or 203 -203 , and therefore 2018 + a 2018+a is either 2219 2219 or 1815 1815 . Since we are looking for the minimal value, the correct answer is 1815 .

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