The following expressions are polynomials? Justify your answer:

$\frac{1}{2 x}$

Factorise the following:

$16 x^{2}+4 y^{2}+9 z^{2}-16 x y-12 y z+24 x z$

Which of the following expressions is a polynomial, state the reason ? If an expression is polynomial, state whether it is a polynomial in one variable or not

$\sqrt{3} x^{2}+\pi x-9$

If $x^{2}-8 x-20=(x+a)(x+b),$ then $a b=\ldots \ldots \ldots$

Without actually calculating the cubes, find the value of :

$(0.2)^{3}-(0.3)^{3}+(0.1)^{3}$