Number of Integer Solutions for Perfect Square

CMAT 2023 · Quantitative Techniques & Data Interpretation · Medium · Number System

The number of all integers nn for which n2+96n^2 + 96 is a perfect square, is

  1. A.

    4

  2. B.

    6

  3. C.

    8

  4. D.

    10

Answer

C

Explanation

Let n2+96=k2⇒k2−n2=96⇒(k−n)(k+n)=96n^2 + 96 = k^2 \Rightarrow k^2 - n^2 = 96 \Rightarrow (k-n)(k+n) = 96. Since 9696 is even, both (k−n)(k-n) and (k+n)(k+n) must be even. Factor pairs of 96 into two even factors: (2,48),(4,24),(6,16),(8,12)(2, 48), (4, 24), (6, 16), (8, 12). Each pair gives 2 solutions for nn (positive and negative). Thus 4×2=84 \times 2 = 8 integer values of nn.

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