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Thread: help!! quadratic program

  1. #1
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    Exclamation help!! quadratic program

    write a method called quadratic that solves quadratic equations and prints their roots. recall that a quadratic equation is a polynomial equation in terms of a variable x of the form ax^2 + bx + c = 0. The formula for solving a quadratic equation is:

    x= -b + or - the square root of b^2 - 4ac/2a

    Please use the example where a =1, b= -7, c=10

    so the roots are 5 and 2.

    i am unsure of how to program this can anyone figure it out??


  2. #2
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    Default Re: help!! quadratic program

    help pleasee

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    Super Moderator helloworld922's Avatar
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    Default Re: help!! quadratic program

    What have you done so far?

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    Default Re: help!! quadratic program

    i wrote the algorithm and started...

    algorithm is
    1. get the numbers for variables a,b and c from the given equation 0= ax^2 + bx +c.
    2. declare the variables with their given numbers.
    3.plug the numbers into the variables for the equation x = -b + the square root of b^2 - 4ac/2a
    and solve for x.
    4.plug the numbers into the variables for the equation x = -b - the square root of b^2 - 4ac/2a
    and solve for x.
    5.print the roots for both equations.
    public class quadratic 
    {
       public static void main (String[] args){
     
          int variable a = 1;
          int variable b = -7;
          int variable c = 10;
     
    system.out.println(compute roots(equation);
    }
     
    public static int(compute roots(variable a, variable b, variable c); {
     
       int roots = variable -b + math.sqrt((variable b * variable b) - (4 * a * c)/(2*a));
     
         return root;
    }
    }
    I know im missing the other equation for the root with subtracting the square root, and i dont know how to say my given equation im using, 0 = x2 -7x +10...in order to declare my ints. maybe you can help me where I went wrong?
    Last edited by helloworld922; October 15th, 2009 at 12:37 AM.

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    Default Re: help!! quadratic program

    You're java syntax is a bit off Also, it's not possible for a method to return 2 values, so I removed the helper method. Don't know if you have to handle imaginary roots, I left that out. I would also highly recommend using doubles when computing quadratic roots

    public class Quadratic 
    {
       public static void main (String[] args){
               double a = 1;
               double b = -7;
               double c = 10;
              // compute positive root
              double positive_root = (-b+Math.sqrt(b*b-4*a*c))/(2*a);
              // compute negative root
              double negative_root = (-b-Math.sqrt(b*b-4*a*c))/(2*a);          
              system.out.println(positive_root + "\n"+negative_root);
         }
    }

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    Default Re: help!! quadratic program

    thanks!! do i have to show that i got the variable a b and c from a certain formula or no??

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    Default Re: help!! quadratic program

    ... they are the coefficients to the quadratic equation. In other words, you (or the user) gets to choose them. I don't see much use in this program, it can only solve one quadratic equation

    Unless your assignment specifically told you to find the solution to only one equation, I would make it so the user could input any values of a,b, and c, and also add support for imaginary roots.

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    Default Re: help!! quadratic program

    okayy so maybe you can help me make it so the user can be in control using the scanner??

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    Default Re: help!! quadratic program

    actuallly i would prefer if it included methods and returned them this way...

    can you look this one over and make any changes to fix it pleaseee
    import java.util.*; //so that I can use Scanner
     
    public class quadratic
    {
       public static void main (String[] args)
       {
          Scanner in = new Scanner(System.in);
     
          System.out.print("Please type a quadratic equation, which you would like to find out the roots.");
     
               double quadratic = in.nextDouble();
               double variablea = in.nextDouble();
               double variableb = in.nextDouble();
               double variablec = in.nextDouble();
     
               // calling the method
               double quadraticanswer = quadratic1(variablea, variableb, variablec);
            }
            // compute positive root
              public static double quadratic1(double a, double b, double c) {
              double positiveroot = (-b+Math.sqrt(b*b-4*a*c))/(2*a);
              return positiveroot;
            }
     
              // compute negative root
              public static double quadratic2(double a, double b, double c) {
              double negativeroot = (-b-Math.sqrt(b*b-4*a*c))/(2*a);
              return negativeroot;
              }
    }
    Last edited by helloworld922; October 15th, 2009 at 07:40 PM.

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    Default Re: help!! quadratic program

    I think you might run into a problem by naming a variable quadratic and the class quadratic... not positive on this. As a general rule, always name classes starting with upper case letters, and variables/methods starting with lower case letters (the one exception being constructors, they must have the same name as the class, so should start with an upper-case letter).

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    Default Re: help!! quadratic program

    Use following code
    Scanner keyb = new Scanner(in);
    int a = keyb.nextInt();
    int b = keyb.nextInt();
    int c = keyb.nextInt();
    double d = pow(b,2);
    double f = sqrt(d-(4*a*c));
    double g = (-b+f)/2;
    double h = (-b-f)/2;
    out.printf("The Roots are %1.2f,%1.2f\n",g,h);


    This code works, trust me. It's even formattted.
    Last edited by helloworld922; October 15th, 2009 at 09:11 PM.

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    Default Re: help!! quadratic program

    To be honest, you need to follow a good naming convention as helloworld said...
    public class _ {
     
    	private static int _ = 6;
     
    	public _(){
    		String _ = "Hello";
    		System.out.println(_ + this._);
    	}
     
    	public static void main(String[] args) {
    		_ _ = new _();
    		_._ = 60;
    		System.out.println(_._);
    		System.out.println(_._(_));
    	}
     
    	public String _(_ _){
    		 return Integer.toString(_._);
    	}
     
    }
    Last edited by Freaky Chris; October 16th, 2009 at 10:09 AM.
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

  13. #13
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    Default Re: help!! quadratic program

    :O

    public class 
    {
         public ()
         {
              System.out.println("No!");
         }
    }

  14. #14
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    Default Re: help!! quadratic program

    Hmm, I have the same problem. Here's my code:

    import java.util.Scanner;
     
    public class Assignment2
    {
       public static void main (String[] args)
       {
          Scanner in = new Scanner(System.in);
     
    		System.out.println("This program computes the roots of a Quadratic Equation.");
     
    		System.out.println();
     
     
               System.out.println("Please input coefficient A.");
               double coeffA = in.nextDouble();
               System.out.println("Please input coefficient B.");
               double coeffB = in.nextDouble();
               System.out.println("Please input coefficient C.");
               double coeffC = in.nextDouble();
     
               // calls the method
               double quadraticAnswer1 = quadratic1(coeffA, coeffB, coeffC);
               double quadraticAnswer2 = quadratic2(coeffA, coeffB, coeffC);
     
               System.out.println("The roots of the equation are " + quadraticAnswer1 + " and " + quadraticAnswer2);
            }
              // computes positive root
              public static double quadratic1(double a, double b, double c) {
              double posRoot = (-b+Math.sqrt(b*b-4*a*c))/(2*a);
              return posRoot;
            }
     
              // computes negative root
              public static double quadratic2(double a, double b, double c) {
              double negRoot = (-b-Math.sqrt(b*b-4*a*c))/(2*a);
              return negRoot;
              }
    }

    But when I run the Program, my program says this: "The results are NaN and NaN" What the Hell does NaN mean?

  15. #15
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    Default Re: help!! quadratic program

    You tried to take the square root of a negative number. NaN stands for "not a number", which technically isn't true. It's just not a real number, but there are imaginary roots.