using System;

using org.matheval;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Expression expression = new Expression("sin(pi/2+x)-cos(x) = a");

        //validate expression

        List<String> errors = expression.GetError();

        if (errors.Count == 0)

        {

         // get variables

         List<String> variables = expression.getVariables();

         foreach (String variable in variables)

         {

          Console.WriteLine(variable); // will print x, a

         }

        }

​

    }

}