 Therefore, "a"2 must be even, and because the square of an odd number is odd, that in turn implies that "a" is itself even — which means that "b" must be odd because a/b is in lowest terms.On the other hand, if "a" is even, then "a"2 is a multiple of 4.If "a"2 is a multiple of 4 and "a"2 = 2"b"2, then 2"b"2 is a multiple of 4, and therefore "b"2 must be even, which means that so is "b" too.