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How many pairs of natural numbers is there the difference of whose squares are 45.

a) 1
b) 2
c) 3
d) 4

Answer: c
Explanation: (x2 – y2) = 45
(x – y)(x + y) = 45
The factors of 45 possibles are 15, 3, 9, 5, 1 and 45
Hence, numbers are 9 and 6 or 7 and 2 or 23 and 22
Number of such pairs = 3

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