$A = \{ x:x \ne x\} $ represents

Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 4\, ......... \, A $

Write the following sets in roster form :

$\mathrm{E} =$ The set of all letters in the world $\mathrm{TRIGONOMETRY}$

List all the elements of the following sers :

$D = \{ x:x$ is a letter in the word $"\mathrm{LOYAL}" $ $\} $

Write the following intervals in set-builder form :

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