One such a value of "a" comes from the equation
5a - 4 = a
5a - a = 4
4a = 4
a = 4/4 = 1.
Other such a value of "a" comes from the equation
5a - 4 = -a
5a + a = 4
6a = 4
a = = .
The product of these values, 1 and , is . ANSWER