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Maximum and Minimum value of a quadratic function
• Last Updated : 22 Apr, 2021

Given a quadratic function ax2 + bx + c. Find the maximum and minimum value of the function possible when x is varied for all real values possible.

Examples:

```Input: a = 1, b = -4, c = 4
Output:
Maxvalue = Infinity
Minvalue = 0
Quadratic function given is x2 -4x + 4
At x = 2, value of the function is equal to zero.

Input: a = -1, b = 3, c = -2
Output:
Maxvalue = 0.25
Minvalue = -Infinity```

Approach:

``` Q(x)=ax2 + bx + c.
=a(x + b/(2a))2      +     c-b2/(4a).
first part             second part```

The function is broken into two parts.
The first part is a perfect square function. There can be two cases:

1. Case 1: If value of a is positive.
• The maximum value would be equal to Infinity.
• The minimum value of the function will come when the first part is equal to zero because the minimum value of a square function is zero.
2. Case 2: If value of a is negative.
• The minimum value would be equal to -Infinity.
• Since a is negative, the task to maximize the negative square function. Again maximum value of a negative square function would be equal to zero as it would be a negative value for any other value of x.

The second part is a constant value for a given quadratic function and hence cannot change for any value of x. Hence, it will be added in both cases. Hence, the answer to the problem is:

```If a > 0,
Maxvalue = Infinity
Minvalue = c - b2 / (4a)
If a < 0,
Maxvalue = c - b2 / (4a)
Minvalue = -Infinity```

Below is the implementation of the above approach:

C++

 `// C++ implementation of the above approach``#include ``using` `namespace` `std;` `// Function to print the Maximum and Minimum``// values of the quadratic function``void` `PrintMaxMinValue(``double` `a, ``double` `b, ``double` `c)``{` `    ``// Calculate the value of second part``    ``double` `secondPart = c * 1.0 - (b * b / (4.0 * a));` `    ``// Print the values``    ``if` `(a > 0) {` `        ``// Open upward parabola function``        ``cout << ``"Maxvalue = "``             ``<< ``"Infinity\n"``;``        ``cout << ``"Minvalue = "` `<< secondPart;``    ``}``    ``else` `if` `(a < 0) {` `        ``// Open downward parabola function``        ``cout << ``"Maxvalue = "` `<< secondPart << ``"\n"``;``        ``cout << ``"Minvalue = "``             ``<< ``"-Infinity"``;``    ``}``    ``else` `{` `        ``// If a=0 then it is not a quadratic function``        ``cout << ``"Not a quadratic function\n"``;``    ``}``}` `// Driver code``int` `main()``{``    ``double` `a = -1, b = 3, c = -2;` `    ``PrintMaxMinValue(a, b, c);` `    ``return` `0;``}`

Java

 `// Java implementation of the above approach``import` `java.util.*;` `class` `GFG``{` `    ``// Function to print the Maximum and Minimum``    ``// values of the quadratic function``    ``static` `void` `PrintMaxMinValue(``double` `a, ``double` `b, ``double` `c)``    ``{` `        ``// Calculate the value of second part``        ``double` `secondPart = c * ``1.0` `- (b * b / (``4.0` `* a));` `        ``// Print the values``        ``if` `(a > ``0``)``        ``{` `            ``// Open upward parabola function``            ``System.out.print(``"Maxvalue = "``                    ``+ ``"Infinity\n"``);``            ``System.out.print(``"Minvalue = "` `+ secondPart);``        ``}``        ``else` `if` `(a < ``0``)``        ``{` `            ``// Open downward parabola function``            ``System.out.print(``"Maxvalue = "` `+ secondPart + ``"\n"``);``            ``System.out.print(``"Minvalue = "``                    ``+ ``"-Infinity"``);``        ``}``        ``else``        ``{` `            ``// If a=0 then it is not a quadratic function``            ``System.out.print(``"Not a quadratic function\n"``);``        ``}``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``double` `a = -``1``, b = ``3``, c = -``2``;` `        ``PrintMaxMinValue(a, b, c);``    ``}``}` `// This code is contributed by Rajput-Ji`

Python3

 `# Python3 implementation of the above approach` `# Function to print the Maximum and Minimum``# values of the quadratic function``def` `PrintMaxMinValue(a, b, c) :` `    ``# Calculate the value of second part``    ``secondPart ``=` `c ``*` `1.0` `-` `(b ``*` `b ``/` `(``4.0` `*` `a));``    ` `    ``# Print the values``    ``if` `(a > ``0``) :``        ` `        ``# Open upward parabola function``        ``print``(``"Maxvalue ="``, ``"Infinity"``);``        ``print``(``"Minvalue = "``, secondPart);``        ` `    ``elif` `(a < ``0``) :``        ` `        ``# Open downward parabola function``        ``print``(``"Maxvalue = "``, secondPart);``        ``print``(``"Minvalue ="``, ``"-Infinity"``);``        ` `    ``else` `:``        ` `        ``# If a=0 then it is not a quadratic function``        ``print``(``"Not a quadratic function"``);` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:``    ``a ``=` `-``1``; b ``=` `3``; c ``=` `-``2``;` `    ``PrintMaxMinValue(a, b, c);` `# This code is contributed by AnkitRai01`

C#

 `// C# implementation of the above approach``using` `System;` `class` `GFG``{``    ` `    ``// Function to print the Maximum and Minimum``    ``// values of the quadratic function``    ``static` `void` `PrintMaxMinValue(``double` `a, ``double` `b, ``double` `c)``    ``{` `        ``// Calculate the value of second part``        ``double` `secondPart = c * 1.0 - (b * b / (4.0 * a));` `        ``// Print the values``        ``if` `(a > 0)``        ``{` `            ``// Open upward parabola function``            ``Console.Write(``"Maxvalue = "``                    ``+ ``"Infinity\n"``);``            ``Console.Write(``"Minvalue = "` `+ secondPart);``        ``}``        ``else` `if` `(a < 0)``        ``{` `            ``// Open downward parabola function``            ``Console.Write(``"Maxvalue = "` `+ secondPart + ``"\n"``);``            ``Console.Write(``"Minvalue = "``                    ``+ ``"-Infinity"``);``        ``}``        ``else``        ``{` `            ``// If a=0 then it is not a quadratic function``            ``Console.Write(``"Not a quadratic function\n"``);``        ``}``    ``}` `    ``// Driver code``    ``static` `public` `void` `Main ()``    ``{``        ``double` `a = -1, b = 3, c = -2;``        ``PrintMaxMinValue(a, b, c);``    ``}``}` `// This code is contributed by ajit.`

Javascript

 ``
Output:
```Maxvalue = 0.25
Minvalue = -Infinity```

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