At what values of [[$ x $]] are the expressions defined?

a) [[$ \sqrt {x – 2} $]]

The expression is defined when [[$ x $]] ≥

b) [[$ \sqrt {x + 2} $]]

The expression is defined when [[$ x $]] ≥

c) [[$ \sqrt {1 – x} $]]

The expression is defined when [[$ x $]] ≤

d) [[$ \sqrt {x^2 + 3} $]]

The expression is defined with