# Check if three straight lines are concurrent or not

Given three lines equation,

a_{1}**x** + b_{1}**y** + c_{1} = 0

a_{2}**x** + b_{2}**y** + c_{2} = 0

a_{3}**x** + b_{3}**y** + c_{3} = 0

The task is to check whether the given three lines are concurrent or not. Three straight lines are said to be concurrent if they pass through a point i.e., they meet at a point.

Examples:

Input : a_{1}= 2, b_{1}= -3, c_{1}= 5 a_{2}= 3, b_{2}= 4, c_{2}= -7 a_{3}= 9, b_{3}= -5, c_{3}= 8 Output : Yes Input : a_{1}= 2, b_{1}= -3, c_{1}= 5 a_{2}= 3, b_{2}= 4, c_{2}= -7 a_{3}= 9, b_{3}= -5, c_{3}= 4 Output : No

Let

a_{1}x + b_{1}y + c_{1} = 0 ………. (1)

a_{2}x + b_{2}y + c_{2} = 0 ………. (2)

a_{3}x + b_{3}y + c_{3} = 0 ………. (3)

Suppose the eqn (i) and (ii) intersects at (x_{1}, y_{1}). Then (x_{1}, y_{1}) will satisfy both the equations.

Therefore, solving (i) and (ii) using method of cross-multiplication, we get,

(x_{1}/b_{1}c_{2} – b_{2}c_{1}) = (y_{1}/c_{1}a_{2} – c_{2}a_{1}) = (1/a_{1}b_{2} – a_{2}b_{1})

Therefore,

x_{1} = (b_{1}c_{2} – b_{2}c_{1}/a_{1}b_{2} – a_{2}b_{1}) and

y_{1} = (c_{1}a_{2} – c_{2}a_{1}/a_{1}b_{2} – a_{2}b_{1}), a_{1}b_{2} – a_{2}b_{1} != 0

Therefore, the required coordinates of the point of intersection of the lines (i) and (ii) are

(b_{1}c_{2} – b_{2}c_{1}/a_{1}b_{2} – a_{2}b_{1}, c_{1}a_{2} – c_{2}a_{1}/a_{1}b_{2} – a_{2}b_{1})

For, three of line to be concurrent, (x_{1}, y_{1}) must satisfy the equation (iii) as well.

So,

a_{3}x + b_{3}y + c_{3} = 0

=> a_{3}(b_{1}c_{2} – b_{2}c_{1}/a_{1}b_{2} – a_{2}b_{1}) + b_{3}(c_{1}a_{2} – c_{2}a_{1}/a_{1}b_{2} – a_{2}b_{1}) + c_{3} = 0

=> a_{3}(b_{1}c_{2} – b_{2}c_{1}) + b_{3}(c_{1}a_{2} – c_{2}a_{1}) + c_{3}(a_{1}b_{2} – a_{2}b_{1}) = 0

So, we only need to check if above condition satisfy or not.

Below is the implementation of this approach:

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## C++

`// CPP Program to check if three straight` `// line are concurrent or not` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Return true if three line are concurrent,` `// else false.` `bool` `checkConcurrent(` `int` `a1, ` `int` `b1, ` `int` `c1,` ` ` `int` `a2, ` `int` `b2, ` `int` `c2,` ` ` `int` `a3, ` `int` `b3, ` `int` `c3)` `{` ` ` `return` `(a3 * (b1 * c2 - b2 * c1) +` ` ` `b3 * (c1 * a2 - c2 * a1) + ` ` ` `c3 * (a1 * b2 - a2 * b1) == 0);` `}` `// Driven Program` `int` `main()` `{` ` ` `int` `a1 = 2, b1 = -3, c1 = 5;` ` ` `int` `a2 = 3, b2 = 4, c2 = -7;` ` ` `int` `a3 = 9, b3 = -5, c3 = 8;` ` ` `(checkConcurrent(a1, b1, c1, a2, b2, c2,` ` ` `a3, b3, c3) ? (cout << ` `"Yes"` `) : (cout << ` `"No"` `));` ` ` `return` `0;` `}` |

## Java

`// Java Program to check if three straight` `// line are concurrent or no` `import` `java.io.*;` `class` `GFG {` ` ` `// Return true if three line are concurrent,` ` ` `// else false.` ` ` `static` `boolean` `checkConcurrent(` `int` `a1, ` `int` `b1,` ` ` `int` `c1, ` `int` `a2, ` `int` `b2, ` `int` `c2,` ` ` `int` `a3, ` `int` `b3, ` `int` `c3)` ` ` `{` ` ` `return` `(a3 * (b1 * c2 - b2 * c1) +` ` ` `b3 * (c1 * a2 - c2 * a1) +` ` ` `c3 * (a1 * b2 - a2 * b1) == ` `0` `);` ` ` `}` ` ` ` ` `// Driven Program` ` ` `public` `static` `void` `main (String[] args)` ` ` `{` ` ` `int` `a1 = ` `2` `, b1 = -` `3` `, c1 = ` `5` `;` ` ` `int` `a2 = ` `3` `, b2 = ` `4` `, c2 = -` `7` `;` ` ` `int` `a3 = ` `9` `, b3 = -` `5` `, c3 = ` `8` `;` ` ` ` ` `if` `(checkConcurrent(a1, b1, c1, a2, b2,` ` ` `c2, a3, b3, c3))` ` ` `System.out.println( ` `"Yes"` `);` ` ` `else` ` ` `System.out.println( ` `"No"` `);` ` ` `}` `}` `// This code is contributed by anuj_67.` |

## Python 3

`# Python3 Program to check if three straight` `# line are concurrent or not` `# Return true if three line are concurrent,` `# else false.` `def` `checkConcurrent(a1, b1, c1, a2, b2, c2,` ` ` `a3, b3, c3):` ` ` `return` `(a3 ` `*` `(b1 ` `*` `c2 ` `-` `b2 ` `*` `c1) ` `+` ` ` `b3 ` `*` `(c1 ` `*` `a2 ` `-` `c2 ` `*` `a1) ` `+` ` ` `c3 ` `*` `(a1 ` `*` `b2 ` `-` `a2 ` `*` `b1) ` `=` `=` `0` `)` `# Driven Program` `a1 ` `=` `2` `b1 ` `=` `-` `3` `c1 ` `=` `5` `a2 ` `=` `3` `b2 ` `=` `4` `c2 ` `=` `-` `7` `a3 ` `=` `9` `b3 ` `=` `-` `5` `c3 ` `=` `8` `if` `(checkConcurrent(a1, b1, c1, a2, b2, c2,` ` ` `a3, b3, c3)):` ` ` `print` `(` `"Yes"` `)` `else` `:` ` ` `print` `(` `"No"` `)` `# This code is contributed by Smitha` |

## C#

`// C# Program to check if three straight` `// line are concurrent or no` `using` `System;` `class` `GFG {` ` ` `// Return true if three line are concurrent,` ` ` `// else false.` ` ` `static` `bool` `checkConcurrent(` `int` `a1, ` `int` `b1,` ` ` `int` `c1, ` `int` `a2, ` `int` `b2, ` `int` `c2,` ` ` `int` `a3, ` `int` `b3, ` `int` `c3)` ` ` `{` ` ` `return` `(a3 * (b1 * c2 - b2 * c1) +` ` ` `b3 * (c1 * a2 - c2 * a1) +` ` ` `c3 * (a1 * b2 - a2 * b1) == 0);` ` ` `}` ` ` ` ` `// Driven Program` ` ` `public` `static` `void` `Main ()` ` ` `{` ` ` `int` `a1 = 2, b1 = -3, c1 = 5;` ` ` `int` `a2 = 3, b2 = 4, c2 = -7;` ` ` `int` `a3 = 9, b3 = -5, c3 = 8;` ` ` ` ` `if` `(checkConcurrent(a1, b1, c1, a2, b2,` ` ` `c2, a3, b3, c3))` ` ` `Console.WriteLine( ` `"Yes"` `);` ` ` `else` ` ` `Console.WriteLine( ` `"No"` `);` ` ` `}` `}` `// This code is contributed by anuj_67.` |

## PHP

`<?php` `// PHP Program to check if three straight` `// line are concurrent or not` `// Return true if three line are` `// concurrent, else false.` `function` `checkConcurrent(` `$a1` `, ` `$b1` `, ` `$c1` `,` ` ` `$a2` `, ` `$b2` `, ` `$c2` `,` ` ` `$a3` `, ` `$b3` `, ` `$c3` `)` `{` ` ` `return` `(` `$a3` `* (` `$b1` `* ` `$c2` `- ` `$b2` `* ` `$c1` `) +` ` ` `$b3` `* (` `$c1` `* ` `$a2` `- ` `$c2` `* ` `$a1` `) +` ` ` `$c3` `* (` `$a1` `* ` `$b2` `- ` `$a2` `* ` `$b1` `) == 0);` `} ` ` ` `// Driver Code` ` ` `$a1` `= 2; ` `$b1` `= -3; ` `$c1` `= 5;` ` ` `$a2` `= 3; ` `$b2` `= 4; ` `$c2` `= -7;` ` ` `$a3` `= 9; ` `$b3` `= -5; ` `$c3` `= 8;` ` ` `if` `(checkConcurrent(` `$a1` `, ` `$b1` `, ` `$c1` `, ` `$a2` `, ` `$b2` `,` ` ` `$c2` `, ` `$a3` `, ` `$b3` `, ` `$c3` `))` ` ` `echo` `"Yes"` `;` ` ` `else` ` ` `echo` `"No"` `;` `// This code is contributed by anuj_67.` `?>` |

## Javascript

`<script>` `// Javascript Program to check if three straight` `// line are concurrent or not` `// Return true if three line are concurrent,` `// else false.` `function` `checkConcurrent( a1, b1, c1,` ` ` `a2, b2, c2,` ` ` `a3, b3, c3)` `{` ` ` `return` `(a3 * (b1 * c2 - b2 * c1) +` ` ` `b3 * (c1 * a2 - c2 * a1) + ` ` ` `c3 * (a1 * b2 - a2 * b1) == 0);` `}` `// Driven Program` `a1 = 2, b1 = -3, c1 = 5;` `a2 = 3, b2 = 4, c2 = -7;` `a3 = 9, b3 = -5, c3 = 8;` `(checkConcurrent(a1, b1, c1, a2, b2, c2,` ` ` `a3, b3, c3) ? (document.write( ` `"Yes"` `)) : (document.write( ` `"No"` `)));` `</script>` |

**Output:**

Yes