Make correct statements by filling in the symbols $\subset$ or $ \not\subset $ in the blank spaces:

$\{ x:x$ is an equilateral triangle in a plane $\} \ldots \{ x:x$ is a triangle in the same plane $\} $

Write the following sets in the set-builder form :

$\{ 1,4,9 \ldots 100\} $

Which of the following are examples of the null set

$\{ y:y$ is a point common to any two parallellines $\} $

In each of the following, determine whether the statement is true or false. If it is true, prove it. If it is false, give an example.

If $A \subset B$ and $x \notin B,$ then $x \notin A$

Write the set $A = \{ 1,4,9,16,25, \ldots .\} $ in set-builder form.