can be written
∠
("m angle theta"),
where:
m =
and
=
For 3+i: m =
= 
=
or approx. 18.435 degrees.
Now, to find the square root, just take the square root of m and divide the angle
by two:
sqrt(3+i) =
∠
or approx. =
∠
If you must express this as 'a + bi' form (rectangular form):
a = m * cos(
) = 1.778*cos(9.218) = 1.755
b = m * sin(
) = 1.778*sin(9.218) = 0.285
so
≈
---
EDIT: the notation I used really comes from Electrical Engineering, but keep in mind it is just shorthand for a+bi = 