1. Is x2−25x+x a polynomial? If not, state a reason. 2. Is -2020x a polynomial?...

Step 1
Polynomials:
$\text{Let} a_0$,$a_1$, $a_2$...................$a_n$ and  "n"  be  a  non-negatine   integer
A  polynomial  in  x  is  an  expression  of  the  form,
$\text{it} a_n{x}^n+a_{n-1}{x}^{n-1}+\dots \dots \dots \dots \dots \dots \dots \dots \dots +a_{1}x+a_0$
Step 2
A polynomial is a function with non-negative integral power.
Consider the polynomials,
$x^3+2\sqrt{5x}+x$
It's not polynomials because polynomial have only integral power,
$x^3+2\sqrt{5x}+x=x^3+2{\left(5x\right)}^{\frac{1}{2}}+x$
It 's  not  a  polynomials  because   term $2{\left(5x\right)}^{\frac{1}{2}}$ having  fractional  power.
Step 3
Consider the polynomials,
- 2020x
It is linear polynomials.

Therefore, -2020x is polynomials
Step 4
Consider the polynomials,
$x^{\frac{2}{3}}+3x+1$
It is not a polynomial because the power of “x” $\left(\frac{2}{3}\right)$ having fractional power.

A polynomial only contains integer powers of "x."