If a and b be positive integers such that $$a^2-b^2 = 19$$, then the value of a is
$$a^2-b^2 = 19$$
19 is a prime numberÂ
(a + b)(a - b) = 19 x 1
So a + b = 19
   a - b = 1
Adding both the equations we get 2a = 20
                          a = 10
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