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

Question

17.5k 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 | 17.5k 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;
}