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

Question

2.5k 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 | 2.5k 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;
}