Question 385818
We have


{{{5 = sqrt((3 - (-1))^2 + (1-a)^2)}}}

{{{5 = sqrt(16 + (1-a)^2)}}}

{{{(1-a)^2 = 9}}}

{{{1-a = 3}}} or {{{1-a = -3}}}


a = -2 or 4