Answer:
Possible values of a = 2.58 and -6.58.
Step-by-step explanation:
Using the distance formula
√(3- 1)^2 + (-2-a)^2) = 5
(3- 1)^2 + (-2-a)^2 = 25
4 + 4a + a^2 + 4 = 25
a^2 + 4a - 17 = 0
a = [-4 +/- √(4^2 - 4*1*-17) ] / 2
a = -2 +/- √84 / 2
a = 2.58, -6.58.