Integer roots!

Algebra Level 3

Find the number of integral roots of the following quadratic equation :

x 2 + 7 x 14 ( q 2 + 1 ) = 0 x^2+7x-14(q^2+1)=0

Note: q q is an integer

2 0 Cannot be determined 1

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1 solution

Let the roots of the given quadratic equation be a a and b b .

By Vieta's formula :

a + b = 7 a+b=-7 and a b = 14 ( q 2 + 1 ) ab=-14(q^2+1)

Note that from first condition, if one of the roots is integral , the other one must be integral.

Now, from second condition , we note that a b < 0 ab<0 . WLOG let us assume that a > 0 a>0 and b < 0 b<0 . Now set c = b c=-b so that c > 0 c>0 and the new equations become :

c a = 7 c-a=7 and c a = 14 ( q 2 + 1 ) ca=14(q^2+1)

Let us suppose that both a a and c c are integers

From first condition they must differ by 7 7 . From second equation exactly one of them is a multiple of 7 [ ( q 2 + 1 ) 7 [(q^2+1) can never be a multiple of 7 7 ].

But wait, if both of them differ by 7 7 and one of them is a multiple of 7 7 then other one must also be a multiple of 7 7 , which can never happen.

Hence, the given quadratic equation can never have any integral roots.

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