List all the elements of the following sers :
$A = \{ x:x$ is an odd natural number $\} $
$A = \{ x:x$ is an odd natural number $\} = \{ 1,3,5,7,9……\} $
State whether each of the following set is finite or infinite :
The set of lines which are parallel to the $x\,-$ axis
How many elements has $P(A),$ if $A=\varnothing ?$
What universal set $(s)$ would you propose for each of the following :
The set of isosceles triangles
Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?
$\{ 3,4\} \in A$
