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;
}