Find the value of the polynomial $x^{2}-7 x+12$ at.

$x=3$

Which of the following expressions are polynomials in one variable and which are not $?$ State reason for your answer. If the given expression is a polynomial, state whether it is a polynomial in one variable or not

$x^{3}+y^{3}+z^{3}-3 x y z$

For polynomial $p(x)=x^{3}-3 x^{2}+8 x+12$, $p(-1)=\ldots \ldots \ldots$

Check whether $p(x)$ is a multiple of $g(x)$ or not :

$p(x)=x^{3}-5 x^{2}+4 x-3, \quad g(x)=x-2$

The following expressions are polynomials? Justify your answer:

$\frac{1}{5 x^{-2}}+5 x+7$

Factorise each of the following

$27 x^{3}-8 y^{3}-54 x^{2} y+36 x y^{2}$