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

$x^{2}+2 x y+y^{2}$

Factorise the following quadratic polynomials by splitting the middle term

$x^{2}-3 x-40$

Factorise

$x^{2}+\frac{y^{2}}{4}+\frac{z^{2}}{16}+x y+\frac{y z}{4}+\frac{z x}{2}$

With the help of the remainder theorem, find the remainder when the polynomial $x^{3}+x^{2}-26 x+24$ is divided by each of the following divisors

$x-4$

$\ldots \ldots$ is one of the zeros of $p(x)=x^{3}+7 x^{2}+11 x+5$