Answer:
see explanation
Explanation:
Calculate the distance (d) using the distance formula
d = √ (x₂ - x₁ )² + (y₂ - y₁ )²
with (x₁, y₁ ) = (3, 5) and (x₂, y₂ ) = (1, a)
d =

=

=

Equating d to
, gives
=

Squaring both sides
4 + (a - 5)² = 8 ( subtract 4 from both sides )
(a - 5)² = 4 ( take the square root of both sides )
a - 5 = ±
= ± 2 ( add 5 to both sides )
a = 5 ± 2, that is
a = 5 - 2 = 3 OR a = 5 + 2 = 7