An algebra problem by Rahil Sehgal

Algebra Level 4

What is the smallest possible natural number š‘› for which the equation š‘„^{2} āˆ’ š‘›š‘„ + 2014 = 0 has integer roots?


The answer is 91.

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1 solution

Viki Zeta
Mar 10, 2017

x 2 āˆ’ n x + 2014 = 0 ToĀ haveĀ integerĀ roots,Ā discriminantĀ mustĀ beĀ aĀ perfectĀ square n 2 āˆ’ 4 Ɨ 2014 = x 2 n 2 āˆ’ 8056 = x 2 Clearly, n 2 > 8056 āŸ¹ n > 89.7552226893 > 90 UsingĀ trailĀ andĀ errorĀ method,Ā atĀ firstĀ changeĀ usingĀ nĀ =Ā 91 n 2 = 9 1 2 = 8281 āŸ¹ n 2 āˆ’ 8056 = 8281 āˆ’ 8056 = 25 = 5 2 āˆ“ n = 91 , isĀ theĀ smallestĀ possibleĀ valueĀ forĀ ā€™nā€™Ā forĀ whichĀ theĀ equationĀ hasĀ integralĀ roots x^2 - nx + 2014 = 0 \\ \text{To have integer roots, discriminant must be a perfect square} \\ n^2 - 4 \times 2014 = x^2 \\ n^2 - 8056 = x^2 \\ \text{Clearly, } n^2 > 8056 \\ \implies n > 89.7552226893 > 90 \\ \text{Using trail and error method, at first change using n = 91 } \\ n^2 = 91^2 = 8281 \\ \implies n^2 - 8056 = 8281 - 8056 = 25 = 5^2 \\ \boxed{\therefore n = 91, \text{ is the smallest possible value for 'n' for which the equation has integral roots}}

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