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;
}