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

Question

9.5k 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 | 9.5k 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;
}