Monday, February 19, 2024

Find all positive integers x such that there exists a positive integer y satisfying: 1/x + 1/y = 1/7

 

Find all positive integers x such that there exists a positive integer y satisfying: 1/x + 1/y = 1/7

Answer.

1/x + 1/y = 1/7

(x+y)/xy = 1/7

7x + 7y = xy

xy - 7x - 7y = 0

x(y-7) - 7(y-7) = 49

(x-7)(y-7) = 49

Thus satisfying values are:

49   *   1

     1   *   49

   7   *   7

So values of x and y can be, (42, 8), (8, 42), (14, 14).

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