At what value of [[$ x $]] is the rational expression defined?

a) [[$ \displaystyle\frac {x} {x} $]]

Answer: The expression is defined when [[$ x $]] ≠ .

b) [[$ \displaystyle\frac {2 + x} {x + 1} $]]

Answer: The expression is defined when [[$ x $]] ≠ .

c) [[$ \displaystyle\frac {-x - 1} {2x} $]]

Answer: The expression is defined when [[$ x $]] ≠ .

d) [[$ \displaystyle\frac {5x} {x - 3} $]]

Answer: The expression is defined when [[$ x $]] ≠ .