public XEquation(String equation){
		equ = new Equation(equation);
		Vector<Variable> variables = equ.getVariables();
		if(variables.size()==0){
			x = new Variable("x");
		}
		else{
			if(variables.size()!=1)
				throw new EquationException("Invalid X Equation: " + equation);
			x = variables.firstElement();
			if(!x.getName().equals("x"))
				throw new EquationException("Invalid X Equation: " + equation);
		}
	}