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Find the foot of perpendicular of a point in a 3 D plane
• Last Updated : 11 May, 2021

Given a point (x1, y1, z1) in 3-D and coefficients of the equation of plane, we have to find the foot of perpendicular of a point in a 3 D plane.
Examples:

Input: a = 1, b = -2, c = 0, d = 0, x = -1, y = 3, z = 4
Output: x2 = 0.4 y2 = 0.2 z2 = 4.0
Input: a = 2, b = -1, c = 1, d = 3, x = 1, y = 3, z = 4
Output: x2 = -1.0 y2 = 4.0 z2 = 3.0 Approach: Equation of plane is given as ax + by + cz + d = 0. Therefore, the direction ratios of the normal to the plane are (a, b, c). Let N be the foot of perpendicular from given point to the given plane so, line PN has directed ratios (a, b, c) and it passes through P(x1, y1, z1).
The equation of line PN will be as:-

(x – x1) / a = (y – y1) / b = (z – z1) / c = k

Hence any point on line PN can be written as:-

x = a * k + x1
y = b * k + y1
z = c * k + z1

since N lies in both line and plane so will satisfy(ax + by + cz + d = 0).

=>a * (a * k + x1) + b * (b * k + y1) + c * (c * k + z1) + d = 0.
=>a * a * k + a * x1 + b * b * k + b * y1 + c * c * k + c * z1 + d = 0.
=>(a * a + b * b + c * c)k = -a * x1 – b * y1 – c * z1 – d.
=>k = (-a * x1 – b * y1 – c * z1 – d) / (a * a + b * b + c * c).

Now, the coordinates of Point N in terms of k will be:-

x2 = a * k + x1
y2 = b * k + y1
z2 = c * k + z1

Below is the implementation of the above:

## C++

 `// C++ program to find``// foot of perpendicular``// of a point in a 3 D plane.``#include ``#include ``#include ``#include ``using` `namespace` `std;` `// Function to find foot of perpendicular``void` `foot(``float` `a, ``float` `b,``          ``float` `c, ``float` `d,``          ``float` `x1, ``float` `y1,``          ``float` `z1)``{``    ``float` `k = (-a * x1 - b * y1 - c * z1 - d) / (``float``)(a * a + b * b + c * c);``    ``float` `x2 = a * k + x1;``    ``float` `y2 = b * k + y1;``    ``float` `z2 = c * k + z1;` `    ``std::cout << std::fixed;``    ``std::cout << std::setprecision(1);``    ``cout << ``" x2 = "` `<< x2;``    ``cout << ``" y2 = "` `<< y2;``    ``cout << ``" z2 = "` `<< z2;``}` `// Driver Code``int` `main()``{``    ``float` `a = 1;``    ``float` `b = -2;``    ``float` `c = 0;``    ``float` `d = 0;``    ``float` `x1 = -1;``    ``float` `y1 = 3;``    ``float` `z1 = 4;` `    ``// function call``    ``foot(a, b, c, d, x1, y1, z1);``    ``return` `0;``}``// This code is contributed  by Amber_Saxena.`

## Java

 `// Java program to find``// foot of perpendicular``// of a point in a 3 D plane.``import` `java.util.*;``import` `java.text.*;` `class` `solution``{` `// Function to find foot of perpendicular``static` `void` `foot(``float` `a, ``float` `b,``        ``float` `c, ``float` `d,``        ``float` `x1, ``float` `y1,``        ``float` `z1)``{``    ``float` `k = (-a * x1 - b * y1 - c * z1 - d) / (``float``)(a * a + b * b + c * c);``    ``float` `x2 = a * k + x1;``    ``float` `y2 = b * k + y1;``    ``float` `z2 = c * k + z1;``    ``DecimalFormat form = ``new` `DecimalFormat(``"0.0"``);``    ``System.out.print(``" x2 = "` `+form.format(x2));``    ``System.out.print(``" y2 = "` `+form.format(y2));``    ``System.out.print( ``" z2 = "` `+form.format(z2));``}` `// Driver Code``public` `static` `void` `main(String arr[])``{``    ``float` `a = ``1``;``    ``float` `b = -``2``;``    ``float` `c = ``0``;``    ``float` `d = ``0``;``    ``float` `x1 = -``1``;``    ``float` `y1 = ``3``;``    ``float` `z1 = ``4``;` `    ``// function call``    ``foot(a, b, c, d, x1, y1, z1);` `}``}`

## Python3

 `# Python3 program to find``# foot of perpendicular``# of a point in a 3 D plane.` `# Function to find foot of perpendicular``def` `foot(a, b, c, d, x1, y1, z1) :` `    ``k ``=` `(``-``a ``*` `x1 ``-` `b ``*` `y1 ``-` `c ``*` `z1 ``-` `d) ``/` `(a ``*` `a ``+` `b ``*` `b ``+` `c ``*` `c);``    ``x2 ``=` `a ``*` `k ``+` `x1;``    ``y2 ``=` `b ``*` `k ``+` `y1;``    ``z2 ``=` `c ``*` `k ``+` `z1;` `    ``print``(``"x2 ="``,``round``(x2,``1``))``    ``print``(``"y2 ="``,``round``(y2,``1``))``    ``print``(``"z2 ="``,``round``(z2,``1``))`  `# Driver Code``if` `__name__ ``=``=` `"__main__"` `:` `    ``a ``=` `1``    ``b ``=` `-``2``    ``c ``=` `0``    ``d ``=` `0``    ``x1 ``=` `-``1``    ``y1 ``=` `3``    ``z1 ``=` `4` `    ``# function call``    ``foot(a, b, c, d, x1, y1, z1)` `# This code is contributed by Ryuga`

## C#

 `// C# program to find``// foot of perpendicular``// of a point in a 3 D plane.``using` `System;``using` `System.Globalization;` `class` `GFG``{` `// Function to find foot of perpendicular``static` `void` `foot(``float` `a, ``float` `b,``        ``float` `c, ``float` `d,``        ``float` `x1, ``float` `y1,``        ``float` `z1)``{``    ``float` `k = (-a * x1 - b * y1 - c * z1 - d) /``                ``(``float``)(a * a + b * b + c * c);``    ``float` `x2 = a * k + x1;``    ``float` `y2 = b * k + y1;``    ``float` `z2 = c * k + z1;``    ``NumberFormatInfo form = ``new` `NumberFormatInfo();``    ``form.NumberDecimalSeparator = ``"."``;``    ``Console.Write(``" x2 = "` `+ x2.ToString(form));``    ``Console.Write(``" y2 = "` `+ y2.ToString(form));``    ``Console.Write( ``" z2 = "` `+ z2.ToString(form));``}` `// Driver Code``public` `static` `void` `Main(String []arr)``{``    ``float` `a = 1;``    ``float` `b = -2;``    ``float` `c = 0;``    ``float` `d = 0;``    ``float` `x1 = -1;``    ``float` `y1 = 3;``    ``float` `z1 = 4;` `    ``// function call``    ``foot(a, b, c, d, x1, y1, z1);``}``}` `// This code contributed by Rajput-Ji`

## PHP

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## Javascript

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Output:
`x2 = 0.4 y2 = 0.2 z2 = 4.0`

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