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;
}