The zero of the polynomial $5x - 10$ is:

Is the following expression a polynomial? Justify your answer:
$\frac{1}{2x}$

Expand $(x+2t)(x-5t)$.

Are the following expressions polynomials? Justify your answer:
$\frac{1}{7} a^{3}-\frac{2}{\sqrt{3}} a^{2}+4 a-7$

If $a+b+c=0,$ then the value of $a^{3}+b^{3}+c^{3}$ is equal to

Which of the following expressions are polynomials in one variable and which are not? State the reason for your answer. If the given expression is a polynomial,state whether it is a polynomial in one variable or not.
$x^{2} + x - 3 + \frac{4}{x}$