List all the elements of the following sers :
$E = \{ x:x$ is a month of a year not having $ 31 $ days ${\rm{ }}\} $
Consider the sets
$\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$
Insert the symbol $\subset$ or $ \not\subset $ between each of the following pair of sets:
$A, \ldots B$
Assume that $P(A)=P(B) .$ Show that $A=B$.
How many elements has $P(A),$ if $A=\varnothing ?$
Write the solution set of the equation ${x^2} + x - 2 = 0$ in roster form.