Hi.I'd like to ask a question about polynomal equations. http://www.intmath.com/equations-of-higher-degree/1-polynomial-functions.php here is the solution polynomial function of degree 4. graphically.But I don't understand the method ? How we can use graphic method to solve? or can we use? for example ; x^3+6x^2+15x+18 Can we solve this withous using the factorisation method.