Write the following intervals in set-builder form :

$\left( {6,12} \right]$

Write the set $\{ x:x$ is a positive integer and ${x^2} < 40\} $ in the roster form.

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

Examine whether the following statements are true or false :

$\{ a\}  \in \{ a,b,c\} $

Are the following pair of sets equal ? Give reasons.

$A = \{ x:x$ is a letter in the word ${\rm{FOLLOW }}\} $

$B = \{ y:y$ is a letter in the word $WOLF\} $

State which of the following sets are finite or infinite :

$\{ x:x \in N$ and $2x - 1 = 0\} $