def extract_unknowns(x_dict):
    """
    Extracts unknown variable (sympy expressions) from given dictionary
        
    Args:
        x_dict: One of q_dict, p_dict, z_dict, see module documentation at the top.

    Returns:
        unknowns: list of unknown variables in given dictionary
    """

    all_values = list(x_dict.values())
    list_of_variables = []
    for x in all_values:
        if type(x) != int and len(x.free_symbols) != 0:
            list_of_variables += (list(x.free_symbols))

    unknowns = list(set(list_of_variables))
    return unknowns