给定一个二次方程,形式为ax 2 + bx + c,找到它的根。
例子 :
Input : a = 1, b = -2, c = 1
Output : Roots are real and same
1
Input : a = 1, b = 7, c = 12
Output : Roots are real and different
-3, -4
Input : a = 1, b = 1, c = 1
Output : Roots are complex
-0.5 + i1.73205
-0.5 - i1.73205
以下是寻找二次方程式根的直接公式。
有以下重要情况。
If b*b < 4*a*c, then roots are complex
(not real).
For example roots of x2 + x + 1, roots are
-0.5 + i1.73205 and -0.5 - i1.73205
If b*b == 4*a*c, then roots are real
and both roots are same.
For example, roots of x2 - 2x + 1 are 1 and 1
If b*b > 4*a*c, then roots are real
and different.
For example, roots of x2 - 7x - 12 are 3 and 4
下面是上述公式的实现。
C
/* C program to find roots of a quadratic equation */
#include
#include
#include
// Prints roots of quadratic equation ax*2 + bx + x
void findRoots(int a, int b, int c)
{
// If a is 0, then equation is not quadratic, but
// linear
if (a == 0) {
printf("Invalid");
return;
}
int d = b * b - 4 * a * c;
double sqrt_val = sqrt(abs(d));
if (d > 0) {
printf("Roots are real and different \n");
printf("%f\n%f", (double)(-b + sqrt_val) / (2 * a),
(double)(-b - sqrt_val) / (2 * a));
}
else if (d == 0) {
printf("Roots are real and same \n");
printf("%f", -(double)b / (2 * a));
}
else // d < 0
{
printf("Roots are complex \n");
printf("%f + i%f\n%f - i%f", -(double)b / (2 * a),
sqrt_val, -(double)b / (2 * a), sqrt_val);
}
}
// Driver code
int main()
{
int a = 1, b = -7, c = 12;
// Function call
findRoots(a, b, c);
return 0;
}
C++
/* C++ program to find roots of a quadratic equation */
#include
using namespace std;
// Prints roots of quadratic equation ax*2 + bx + x
void findRoots(int a, int b, int c)
{
// If a is 0, then equation is not quadratic, but
// linear
if (a == 0) {
cout << "Invalid";
return;
}
int d = b * b - 4 * a * c;
double sqrt_val = sqrt(abs(d));
if (d > 0) {
cout << "Roots are real and different \n";
cout << (double)(-b + sqrt_val) / (2 * a) << "\n"
<< (double)(-b - sqrt_val) / (2 * a);
}
else if (d == 0) {
cout << "Roots are real and same \n";
cout << -(double)b / (2 * a);
}
else // d < 0
{
cout << "Roots are complex \n";
cout << -(double)b / (2 * a) << " + i" << sqrt_val
<< "\n"
<< -(double)b / (2 * a) << " - i" << sqrt_val;
}
}
// Driver code
int main()
{
int a = 1, b = -7, c = 12;
// Function call
findRoots(a, b, c);
return 0;
}
Java
// Java program to find roots
// of a quadratic equation
import java.io.*;
import static java.lang.Math.*;
class Quadratic {
// Prints roots of quadratic
// equation ax * 2 + bx + x
static void findRoots(int a, int b, int c)
{
// If a is 0, then equation is not
// quadratic, but linear
if (a == 0) {
System.out.println("Invalid");
return;
}
int d = b * b - 4 * a * c;
double sqrt_val = sqrt(abs(d));
if (d > 0) {
System.out.println(
"Roots are real and different \n");
System.out.println(
(double)(-b + sqrt_val) / (2 * a) + "\n"
+ (double)(-b - sqrt_val) / (2 * a));
}
else if (d == 0) {
System.out.println(
"Roots are real and same \n");
System.out.println(-(double)b / (2 * a) + "\n"
+ -(double)b / (2 * a));
}
else // d < 0
{
System.out.println("Roots are complex \n");
System.out.println(-(double)b / (2 * a) + " + i"
+ sqrt_val + "\n"
+ -(double)b / (2 * a)
+ " - i" + sqrt_val);
}
}
// Driver code
public static void main(String args[])
{
int a = 1, b = -7, c = 12;
// Function call
findRoots(a, b, c);
}
}
// This code is contributed by Sumit Kumar.
Python3
# Python program to find roots
# of a quadratic equation
import math
# Prints roots of quadratic equation
# ax*2 + bx + x
def findRoots(a, b, c):
# If a is 0, then equation is
# not quadratic, but linear
if a == 0:
print("Invalid")
return -1
d = b * b - 4 * a * c
sqrt_val = math.sqrt(abs(d))
if d > 0:
print("Roots are real and different ")
print((-b + sqrt_val)/(2 * a))
print((-b - sqrt_val)/(2 * a))
elif d == 0:
print("Roots are real and same")
print(-b / (2*a))
else: # d<0
print("Roots are complex")
print(- b / (2*a), " + i", sqrt_val)
print(- b / (2*a), " - i", sqrt_val)
# Driver Program
a = 1
b = -7
c = 12
# Function call
findRoots(a, b, c)
# This code is contributed by Sharad Bhardwaj.
C#
// C# program to find roots
// of a quadratic equation
using System;
class Quadratic {
// Prints roots of quadratic
// equation ax * 2 + bx + x
void findRoots(int a, int b, int c)
{
// If a is 0, then equation is
// not quadratic, but linear
if (a == 0) {
Console.Write("Invalid");
return;
}
int d = b * b - 4 * a * c;
double sqrt_val = Math.Abs(d);
if (d > 0) {
Console.Write(
"Roots are real and different \n");
Console.Write(
(double)(-b + sqrt_val) / (2 * a) + "\n"
+ (double)(-b - sqrt_val) / (2 * a));
}
// d < 0
else {
Console.Write("Roots are complex \n");
Console.Write(-(double)b / (2 * a) + " + i"
+ sqrt_val + "\n"
+ -(double)b / (2 * a) + " - i"
+ sqrt_val);
}
}
// Driver code
public static void Main()
{
Quadratic obj = new Quadratic();
int a = 1, b = -7, c = 12;
// Function call
obj.findRoots(a, b, c);
}
}
// This code is contributed by nitin mittal.
PHP
0)
{
echo "Roots are real and ".
"different \n";
echo (-$b + $sqrt_val) / (2 * $a) , "\n",
(-$b - $sqrt_val) / (2 * $a);
}
else if ($d == 0)
{
echo "Roots are real and same \n";
echo -$b / (2 * $a);
}
// d < 0
else
{
echo "Roots are complex \n";
echo -$b / (2 * $a) , " + i" ,
$sqrt_val, "\n" , -$b / (2 * $a),
" - i", $sqrt_val;
}
}
// Driver code
$a = 1; $b = -7 ;$c = 12;
// Function call
findRoots($a, $b, $c);
// This code is contributed
// by nitin mittal.
?>
Javascript
输出
Roots are real and different
4.000000
3.000000