What if there is a negative sign before a square root

For example: Find each real-number root.

-√36

√-81

for the first 1 it would just be -1 * the number, so -6

The second one you have to use i ( i = √-1) to get 9i

You find the square root first then make it negative
-√36= -(6) = -6
The next one is a complex number so you have i
√-81= 9(-1) = 9i

-√36 = -6

√-81 = √(81)*(-1) = 9*√-1 = 9i ....... where i is the imaginary unit such that i^2 = -1