The number of pairs of natural numbers, the difference of

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The number of pairs of natural numbers, the difference of whose squares is 45 will be

Let the numbers be x and y where x > y
∴ x² − y² = 45
⇒ (x + y)(x – y) = 45
Now, 45 = 5 × 9
= 15 × 3 = 45 × 1
∴ Number of pairs = 3