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

Question

7.6k 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 | 7.6k 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;
}