Which algebraic expression is a polynomial with a degree of 4?
5x4 + square root of 4x
x5 – 6x4 + 14x3 + x2
9x4 – x3 – x/5
2x4 – 6x4 + 14/x

A polynomial of degree n is an expression of the form:



where a, b, c, ...d, e, f are Real numbers, and any of them can be = 0, except a.
and the degrees, n, n-1, .... are all non-negative integers: {0, 1, 2, 3 ...}

Among our choices, 

the first one,, 

does not fit the polynomial definition, so the expression is not a polynomial.

the second one, is a fifth degree polynomial

the third one,  is a fourth degree polynomial.

the fourth one,  is not a polynomial

 9x4 – x3 – x/5