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# Find normal at a given point on the curve

• Last Updated : 10 May, 2021

Given a curve [ y = x(A – x) ], the task is to find normal at a given point ( x, y) on that curve, where A is an integer number and x, y also any integer.

Examples:

```Input: A = 2, x = 2, y = 0
Output: 2y = x - 2
Since y = x(2 - x)
y = 2x - x^2 differentiate it with respect to x
dy/dx = 2 - 2x  put x = 2, y = 0 in this equation
dy/dx = 2 - 2* 2 = -2
equation  => (Y - 0 ) = ((-1/-2))*( Y - 2)
=> 2y = x -2

Input: A = 3, x = 4, y = 5
Output: Not possible
Point is not on that curve ```

Approach: First we need to find given point is on that curve or not if the point is on that curve then:

1. We need to differentiate that equation that point don’t think too much for differentiation of this equation if you analyze then you find that dy/dx always become A – 2x.
2. Put x, y in dy/dx.
3. Equation of normal is Y – y = -(1/( dy/dx )) * (X – x).

Below is the implementation of the above approach:

## C++

 `// C++ program for find curve``// at given point``#include ``using` `namespace` `std;` `// function for find normal``void` `findNormal(``int` `A, ``int` `x, ``int` `y)``{``    ``// differentiate given equation``    ``int` `dif = A - x * 2;` `    ``// check that point on the curve or not``    ``if` `(y == (2 * x - x * x)) {` `        ``// if differentiate is negative``        ``if` `(dif < 0)``            ``cout << 0 - dif << ``"y = "``                 ``<< ``"x"` `<< (0 - x) + (y * dif);` `        ``else` `if` `(dif > 0)` `            ``// differentiate is positive``            ``cout << dif << ``"y = "``                 ``<< ``"-x+"` `<< x + dif * y;` `        ``// differentiate  is zero``        ``else``            ``cout << ``"x = "` `<< x;``    ``}` `    ``// other wise normal not found``    ``else``        ``cout << ``"Not possible"``;``}` `// Driver code``int` `main()``{``    ``// declare variable``    ``int` `A = 2, x = 2, y = 0;` `    ``// call function findNormal``    ``findNormal(A, x, y);``    ``return` `0;``}`

## Java

 `// Java program for find curve``// at given point` `import` `java.io.*;` `class` `GFG {` `// function for find normal``static` `void` `findNormal(``int` `A, ``int` `x, ``int` `y)``{``    ``// differentiate given equation``    ``int` `dif = A - x * ``2``;` `    ``// check that point on the curve or not``    ``if` `(y == (``2` `* x - x * x)) {` `        ``// if differentiate is negative``        ``if` `(dif < ``0``)``            ``System.out.print( (``0` `- dif) + ``"y = "``                ``+ ``"x"` `+((``0` `- x) + (y * dif)));` `        ``else` `if` `(dif > ``0``)` `            ``// differentiate is positive``            ``System.out.print( dif + ``"y = "``                ``+ ``"-x+"` `+ (x + dif * y));` `        ``// differentiate is zero``        ``else``            ``System.out.print( ``"x = "` `+x);``    ``}` `    ``// other wise normal not found``    ``else``        ``System.out.println( ``"Not possible"``);``}` `       ``// Driver code``    ``public` `static` `void` `main (String[] args) {``        ``// declare variable``    ``int` `A = ``2``, x = ``2``, y = ``0``;` `    ``// call function findNormal``    ``findNormal(A, x, y);;``    ``}``}``// This Code is contributed by inder_verma..`

## Python3

 `# Python 3 program for find curve``# at given point` `# function for find normal``def` `findNormal(A, x, y):``    ` `    ``# differentiate given equation``    ``dif ``=` `A ``-` `x ``*` `2` `    ``# check that point on the curve or not``    ``if` `(y ``=``=` `(``2` `*` `x ``-` `x ``*` `x)):``        ` `        ``# if differentiate is negative``        ``if` `(dif < ``0``):``            ``print``(``0` `-` `dif, ``"y ="``, ``"x"``,``                 ``(``0` `-` `x) ``+` `(y ``*` `dif))` `        ``elif` `(dif > ``0``):``            ` `            ``# differentiate is positive``            ``print``(dif, ``"y ="``, ``"- x +"``,``                        ``x ``+` `dif ``*` `y)` `        ``# differentiate is zero``        ``else``:``            ``print``(``"x ="``, x)` `    ``# other wise normal not found``    ``else``:``        ``print``(``"Not possible"``)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``# declare variable``    ``A ``=` `2``    ``x ``=` `2``    ``y ``=` `0` `    ``# call function findNormal``    ``findNormal(A, x, y)``    ` `# This code is contributed By``# Surendra_Gangwar`

## C#

 `// C# program for find curve``// at given point``using` `System;` `class` `GFG``{``    ` `// function for find normal``static` `void` `findNormal(``int` `A,``                       ``int` `x, ``int` `y)``{``    ``// differentiate given equation``    ``int` `dif = A - x * 2;` `    ``// check that point on``    ``// the curve or not``    ``if` `(y == (2 * x - x * x))``    ``{` `        ``// if differentiate is negative``        ``if` `(dif < 0)``            ``Console.Write((0 - dif) + ``"y = "` `+``                   ``"x"` `+ ((0 - x) + (y * dif)));` `        ``else` `if` `(dif > 0)` `            ``// differentiate is positive``            ``Console.Write(dif + ``"y = "` `+``                          ``"-x + "` `+ (x + dif * y));` `        ``// differentiate is zero``        ``else``            ``Console.Write(``"x = "` `+ x);``    ``}` `    ``// other wise normal not found``    ``else``        ``Console.WriteLine(``"Not possible"``);``}` `// Driver code``static` `public` `void` `Main ()``{``    ``// declare variable``    ``int` `A = 2, x = 2, y = 0;``    ` `    ``// call function findNormal``    ``findNormal(A, x, y);``}``}` `// This code is contributed by ajit`

## PHP

 ` 0)` `            ``// differentiate is positive``            ``echo` `\$dif` `, ``"y = "``,``                 ``"-x+"` `,( ``\$x` `+ ``\$dif` `* ``\$y``);` `        ``// differentiate is zero``        ``else``            ``echo` `"x = "` `, ``\$x``;``    ``}` `    ``// other wise normal not found``    ``else``        ``echo` `"Not possible"``;``}` `// Driver code` `// declare variable``\$A` `= 2;``\$x` `= 2;``\$y` `= 0;` `// call function findNormal``findNormal(``\$A``, ``\$x``, ``\$y``);` `// This code is contributed by ajit``?>`

## Javascript

 ``
Output:
`2y = x-2`

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