I have two problems that I'm not sure if I did them right.

The first one is:

Solve the equation: sqrt z = -1

my answer:

(sqrt z)^2 = -1^2

z= 1

The second one is:

Solve the equation: sqrt 2a = 2

my answer:

(sqrt 2a)^2 = 2^2

2a = 4

Please help me understand this eqations.

Thank you in advance.