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

Question

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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 | 19.7k views

56 Answers

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The Judge · Answer 1 · 2017-11-02 18:13:29

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answered Nov 2, 2017

LinJingYao · Answer 2 · 2017-10-29 01:00:17

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answered Oct 29, 2017 by LinJingYao (-498 points)

LinJingYao · Answer 3 · 2017-10-29 00:56:09

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answered Oct 29, 2017 by LinJingYao (-498 points)

coach · Answer 4 · 2017-10-28 22:32:45

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answered Oct 28, 2017 by coach (-258 points)

coach · Answer 5 · 2017-10-28 22:29:11

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answered Oct 28, 2017 by coach (-258 points)

prog.c: In function 'main':
prog.c:13:20: warning: too many arguments for format [-Wformat-extra-args]
             printf("Roots of %.2fx^2 + %.2fx + 1.00 = 0 are real and different\n",a,b,c);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
prog.c:19:20: warning: too many arguments for format [-Wformat-extra-args]
             printf("Roots of %.2fx^2 + %.2fx + 1.00 = 0 are real and same\n",a,b,c);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
prog.c:24:20: warning: too many arguments for format [-Wformat-extra-args]
             printf("Roots of %.2fx^2 + %.2fx + 1.00 = 0 are complex and different\n",a,b,c);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

commented Oct 28, 2017 by The Judge (4.3k points)

fung2004067 · Answer 6 · 2017-10-28 19:52:22

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answered Oct 28, 2017 by fung2004067 (-214 points)

fung2004067 · Answer 7 · 2017-10-28 19:51:44

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answered Oct 28, 2017 by fung2004067 (-214 points)

fung2004067 · Answer 8 · 2017-10-28 14:26:09

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answered Oct 28, 2017 by fung2004067 (-214 points)

fung2004067 · Answer 9 · 2017-10-28 14:25:06

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answered Oct 28, 2017 by fung2004067 (-214 points)

fung2004067 · Answer 10 · 2017-10-28 14:22:54

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answered Oct 28, 2017 by fung2004067 (-214 points)

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

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