symbolic - Is there an analogue of the Variables command for general expressions?

The command

Variables[poly]

gives me a list of all variables that appear in the expression poly, which involved sums, products, and rational powers. Sadly, it doesn't work for more complicated expressions, such as trigonometric functions. I was wondering if there is another command that can handle expressions such as $\sin(x)+\cos(y)$.

Answer

ClearAll[x, y, z, d, h, p, m, f, g, a, w];


expr = Sin[x] + Cos[y] + z^3 + Exp[d] + h + 3 h^2 + 4 h^3 + 
   Integrate[Exp[p], p] + 
   D[Sin[m]^Exp[f], m]*Series[Sin[g], {g, 0, 3}] + 
   2 (E^a BesselK[0, 2 Sqrt[E^a]]) C[2]/D[Gamma[w], {w, 2}];

Cases[Variables[Level[expr, -1]], x_ /; AtomQ[x] :> x]

(* {a, d, f, g, h, m, p, w, x, y, z} *)

Comments

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plotting - Mathematica: 3D plot based on combined 2D graphs

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