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How many possible values for k [ 0 , 2014 ] k \in [0,2014] . such that the function

f ( x ) = x 2 14 x k f(x) = x^{2} - 14x - k

has 2 integer roots.


The answer is 39.

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1 solution

Solve the quadratic equation and we will get

x = 7 ± 49 + k x = 7 \pm \sqrt{49 + k}

For the roots to be integers, 49 + k 49 + k must be a perfect square but must not exceed 2063 2063

So, the possibilities of 49 + k 49 + k are 7 2 , 8 2 , 9 2 , . . . , 4 5 2 7^{2}, 8^{2}, 9^{2}, ..., 45^{2}

So there are 39 39 possibilities for k k

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