Variables

Variables[poly] gives a list of all independent variables in a polynomial.

Examples

Find variables in polynomial:

Variables[x^2 + 3x*y + z]
(* {x, y, z} *)

Single variable expression:

Variables[a*t^2 + b*t + c]
(* {a, b, c, t} *)

Please visit the official Wolfram Language Reference for more details.