10-26 Exercise 3: Find roots of a quadratic equation

Question

14.8k views

Write a program to find roots of a quadratic equation

A quadratic equation is a second order equation having a single variable. Any quadratic equation can be represented as where a, b and c are constants ( a can't be 0) and x is unknown variable.

寫一個找二次方程的求根程式

For Example

is a quadratic equation where a, b and c are 2, 5 and 3 respectively.

To calculate the roots of quadratic equation we can use below formula. There are two solutions of a quadratic equation.

使用下列公式:

x = (-b + sqrt(D))/(2*a)
x = (-b - sqrt(D))/(2*a)

where, D = (b*b-4*a*c) is Discriminant (判別式), which differentiate the nature of the roots of quadratic equation.

For the complex result (複數根):

realPart = -b/(2*a);
imaginaryPart =sqrt(-D)/(2*a);

Note: We have used sqrt() function to find square root which is in math.h library.

Example input 1:

1 2 1

Example output 1:

Roots of 1.00x^2 + 2.00x + 1.00 = 0 are real and same
x1 = x2 = -1.00

Example input 2:

1 -3 2

Example output 2:

Roots of 1.00x^2 + -3.00x + 2.00 = 0 are real and different
x1 = 2.00
x2 = 1.00

Example input 3:

1 2 2

Example output 3:

Roots of 1.00x^2 + 2.00x + 2.00 = 0 are complex and different
x1 = -1.00+1.00i
x2 = -1.00-1.00i

[Exercise] Coding (C) - asked Oct 26, 2017 in Chapter 5: Selection Statements by semicolon (5.2k points)
ID: 28934 - Available when: 2017-10-26 18:00 - Due to: Unlimited
reopened Oct 26, 2017 by thopd | 14.8k views

56 Answers

Page:

« prev
1
2
3
4
5
6
next »

112233 · Answer 1 · 2017-11-09 17:27:38

Hidden content!
#include        ** * ***** 
#include ** ** *    * * * 

int main()
{
  * * *** *    *  * **  *    * * a, b, c, determinant, x1,x2, realPart, ***      


 * * ****  * ****       **  *  ** * ** **  * %lf    ****** * **  **  &b, &c);


* * **** *   *    **   *  ****      = b*b-4*a*c;

 *  *   * **** **  *******    *  condition for real and different roots


* *  *   *          *  * *  *** * * for real and equal roots
** **     ****** *  * * ****   *  *  (determinant == 0)
 *   ******  ***** *** * * ****
   *  * *******   ** *  *  * * ***     *   * * * *     = x2 = -b/(2*a);
 ********  *  **   *****    ** ** **  ** ** ** ** **   * *  * *  of %.2fx^2 + %.2fx + %.2f = 0 are real and     * *  * * a,b,c);
 * * * *** * *** * *  *** *  **********     ** *     ****  ** ****** = x2 = *** *  * *    x1);
  ** * * * ***  *      * **  ** 

* ****    *  *** *    * * **  ***  ** * *  if * *    *  > 0)
* * *    *  *  * ***  * **
**     *  * *   **  * **    sqrt() function returns square root
**         *   ****** *  ** * ** * *  ** *  *  ** * **  =  ****** ***** ***
  **** *        **  ******   ***  **** *  * * *** * =  ****  ** *  *    *

* *   * * * *  * **    *  *** ** ******     **  * * *  * *** * * *  *   of %.2fx^2 + %.2fx + %.2f = 0 are real and  * **  **   **   
  * *  *  * ** * *  **   ** * ** **    * ****** ** *     **  * =  * * ** **  x1);
  *     * * *  *  **   *** ** ***   *******    *  *    *****  * *    =        * *  x2);
***  **     *  ** *** *** * if roots are not real
 *     *  * *    ***   ** *  *
* **   ***   ** ** ** *  * * 
****  * * ** **   * * **     *   **** ** **  **   * * **  **** = -b/(2*a);
 *  ** *** *  *  * **  ******  *  *** **   *    *   *    ******  ** * = *     ******  ****  
 ***  *   ** *   ** *  *  *** *  *   *    ** ** *  *  *   **  of %.2fx^2 + %.2fx + %.2f = 0 are complex and   *   * **** *  **  a,b,c);
 * ****  *  **   *** *   *   *  *** * *****    * *  * ** *****    =    * *****  * **   realPart, ** ** *   *
  * *** **  ****  **    *****   ** ** *  *    *   **  * ****     = * ** * * ** **   realPart, * **** ** 
* **    * ** ** * ** ****** ** *

 *      ***  *** * * * *  ** 0;
}

answered Nov 9, 2017 by 112233 (-167 points)

112233 · Answer 2 · 2017-11-09 17:17:35

Hidden content!
#include *  ** ** *  
#include * * *  *  *  *

int main()
{
*** *    **  ** ***  *    ***    * *  a, b, c, determinant, x1,x2, realPart,  *    ** 


  **  * * * *** **  ** *** *   **** ** %lf *** *** ** ***** &b, &c);


* *    *  *** ** **** ******  *   = b*b-4*a*c;

 *   ***     * * ***    **  **  condition for real and different roots
*  ** *  * *  **** *** *  **  (determinant > 0)
* *** *   *    ***** *   * * * 
  **** ** **  **     **  ****  * sqrt() function returns square root
 ***** * **** * *   **  *   * * *** **  * *** *    ** **   =  ***** *** *  *   
 *  * *** *****  *   *** ** * *** ******** *** * ** *  ***** =  *   * *     *** * *

 * *  *  ******  * ***   * *  * *   **   * * **   * *  **  **  *** *  of %.2fx^2 + %.2fx + %.2f = 0 are real and   * * *** *    * ** *
***  *   ***    * ** * **** ****   ***  *      * *  *  *  * *** = **** **** *   x1);
  **** *   ******* * *****  *******      ***** * *  * * ** **  *   * **  = **    * **  x2);
** ** *** ****   *****    

******  **** ******* *   *** ** for real and equal roots
* ***** **     ** ** *  * *     if (determinant == 0)
** ** ** ***  *   *** * * *  * 
  * * * *******    * ******* *  * ** * *    * **** = x2 = -b/(2*a);
* * ***  * * ** *   **   ***  **   *  **   ***       ** * * ** * ***  of %.2fx^2 + %.2fx + %.2f = 0 are real and     * * ***  a,b,c);
** ****     **** ** * * * ** *  *** **  ***   *  *** * *  **     *   *    = x2 =     **  * *  x1);
* *****    * *** *  * **  **  * 

* ** *  **  * * *** *  ** ** if roots are not real
* * * ****    *  *  *  **  * ***  * 
*   * *    *   ** *  * ****
     ** *   **** ** ***    *** *** * *    *  **** * ** *** * * = -b/(2*a);
* ***     *  ** *   *** ***  ****  * **  * *** *  * ** *  *** = **    * ***    
* * ** * **  **  ****  ** ** **  *   *  ** *   *   *       ** ****** *      of %.2fx^2 + %.2fx + %.2f = 0 are complex and **    * ***  *  a,b,c);
**  * *    ** *** ****** *  * * *   *  **** *     * ** *** **     ** * = **  **   ** *   ** realPart,  ** *  *
** * * *  ** *   *****     * * * *********** *      ****    **   ***     =    *  ** *   * realPart, ***** *  * 
*  * **** * ******    *   **

*  *  ******   * ***** ***   *       0;
}

answered Nov 9, 2017 by 112233 (-167 points)

garrylin2 · Answer 3 · 2017-11-02 19:54:55

Hidden content!
**  * *   ***     **  * *
* ** *   ****  ** * 
int main(void)
{
  *   * ** * * **     * ***   a,b,c,d;
 **  ****** * * *     **  ***  ***  * *  %f *** * **   ***  *   **** ***** **
*     **    ***  *   * *   ***
 ***  * * *** *   *** ***   ** ** *
** *** *  * * **  *   *    ****   *  *    **** ***  ***   **   *** * * of %.2fx^2 + %.2fx + %.2f = 0 are real and   ***    = %.2f\nx2 =    *****      + **   ***  * -   ***  *  
*  *  *     *  *   * **     **
*****    * ********  **  ***   (d==0){
       *   *** **        * *   **  ***    *  *   ***  *    *** *  of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 =  * * ** ** * **   +  ***    *  
** *** ** **      *  *    *
   ****  **   * *   *** ***** ** (d<0) {
 *     * * ***** *       **  * **** ***  *** *  **       of %.2fx^2 + %.2fx + %.2f = 0 are complex and *  ***** =   *     =  * *** *   ** *  *  **    ***      ********
    * * ******** **  ** * 
}

answered Nov 2, 2017 by garrylin2 (-204 points)

garrylin2 · Answer 4 · 2017-11-02 19:53:31

Hidden content!
 ***** * ******    * * 
** ** **   **** **   *  *
int main(void)
{
**  *  * **  *** * * * **   *     a,b,c,d;
   * * *****  * * * ***  * * *     * *  *  *  %f *  **    *  * *  *  **  *    *  
*****   *  *   *** ***  ** ** *   **  
 *   ***** * *    ******  **  ** * (d>0){
*   **     *** ********  ***    ** *  * ** *    **  *      *   *** of %.2fx^2 + %.2fx + %.2f = 0 are real and **** * *  = %.2f\nx2 =   *   ***  *  + * **  **** * - *  * **   
* *    **  *   ***  * *  ***
 * *  ** ***  * **  * * *  *  (d==0){
*  *  *  ** **  ***   *** **  ***    *** *  *  ** *    * * * *  *   of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = ***** * *  ** + ******  ******
 ***  * ***  * * **** *  *  * *
 *** * * * **  * * *******  {
  * *** ** * **  **      *********         *  **  *   * **   * *   *** ** of %.2fx^2 + %.2fx + %.2f = 0 are complex and * **** *    = *  **    =    ***  *   **  ** * ** * **** *  **  **    *   ** 
    * **  * ******** 
}

answered Nov 2, 2017 by garrylin2 (-204 points)

rick · Answer 5 · 2017-11-02 19:34:07

prog.c: In function 'main':
prog.c:5:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
     scanf("%f %f %f",&a,&b,&c);
     ^~~~~
prog.c:5:5: warning: incompatible implicit declaration of built-in function 'scanf'
prog.c:5:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
prog.c:13:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are real and different\nx1=%.2f\nx2=%.2f\n",a,b,c,x1,x2);
         ^~~~~~
prog.c:13:9: warning: incompatible implicit declaration of built-in function 'printf'
prog.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
prog.c:17:9: warning: incompatible implicit declaration of built-in function 'printf'
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = %.2f",a,b,c,x1);
         ^~~~~~
prog.c:17:9: note: include '<stdio.h>' or provide a declaration of 'printf'
prog.c:21:9: warning: incompatible implicit declaration of built-in function 'printf'
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are complex and different\nx1 = %.2f+%.2fi\nx2 = %.2f-%.2fi",a,b,c,x3,x4,x3,x4);
         ^~~~~~
prog.c:21:9: note: include '<stdio.h>' or provide a declaration of 'printf'

rick · Answer 6 · 2017-11-02 19:28:09

Hidden content!
#include<stdio.h>
#include<math.h>
int main()
{
      *    *  *  ***** * * * **   a,b,c,d,x1,x2,x3,x4;
**   **  * * *   ** * **    ***  ** **  %f  * * * ** *    *  *  ** *  *** 
   ***** **      * **   ** * ** * *
 **  ** **  * *** **     ** *** ** * * **
 **    * ** *  **  **** *   ** ***  * *** *
  * **   *  ****   * *  *     **  *  *
* * *  **** * **    *  *** * *   * * *
**   ** *****     * *   ***  ***    *   **    * * ***
    **  * **** ** ****    
**** *   *******  *** * *** *** *       * ***  * * *   * *  * * *  of %.2fx^2 + %.2fx + %.2f = 0 are real and  ** **  *   * ******     * 
* **   ** ** *****  ** * *** 
** * *** ***   ** ***   *      * *****  ****    *** *  **  
  *  *** ** *     **** ******
    * *   * **  ****          *    * *    *  * * *   *   * ** *  ***    of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = %.2f",a,b,c,x1);
 *** *****   **  *    **  
**** * **  **    ***   ***  * * *** ****  *** *  * ** * * 
** **   * *    **    ** **
*** **   *** * *****  * *** ** *   *  * * *  **       ***   * *  *   of %.2fx^2 + %.2fx + %.2f = 0 are complex and different\nx1 = %.2f + %.2fi\nx2 = %.2f -  * ** *  ***  ********    * 
 **    *  *  **   **   *
*   ***   *   ** **      *  *   * 0;
}