Is each expression a polynomial?

2x^4+12x+4

x^3+4x

3/x^4-6x^3

x^4/3-6

Given first equation,

(1) 2x^⁴+12x+4

it's a polynomial of degree (4)

known as Tetra polynomial

(2) x^³+4x

it's a polynomial of degree (3)

known as cubic polynomial

(3) 3/x^⁴-6x³

it's not a polynomial because of power of X is (-4) which a negative
so it's not a polynomial

(4) x^⁴/3-6

it's a polynomial of degree (4)

known as Tetra polynomial