math.php

<?php 
$x = [];
$y = [];

// triangle #1 left
$x1[1] = -1;
$y1[1] = -1;

$x1[2] = -1;
$y1[2] = 0;

$x1[3] = 0;
$y1[3] = 0;

// triangle #2 right
$x2[1] = 0;
$y2[1] = 0;

$x2[2] = 1;
$y2[2] = 0;

$x2[3] = 1;
$y2[3] = -1;

// square 
// left top angle
$X[1] = -1;
$Y[1] = 1; // placed on X axis

// right bottom angle
$X[2] = 1;
$Y[2] = 0;

$dot =	[
			'x' => rand(-10, 10)/10,
			'y' => rand(-10, 10)/10
		];


if ($dot['y'] < 0) {
	// under square, doing with triangles
	$ans = inTrinagle($x1[1], $y1[1], $x1[2], $y1[2], $x1[3], $y1[3], $dot['x'], $dot['y']);
	if (($ans['a'] >= 0 && $ans['b'] >= 0 && $ans['c'] >= 0) || ($ans['a'] <= 0 && $ans['b'] <= 0 && $ans['c'] <= 0)) {
		printScrTriang($ans['a'], $ans['b'], $ans['c'], $dot['x'], $dot['y'], 'Found in triangle #1 !!!111один!1упчяка');
		die;
	} else {
		// nope, doing with second triangle
		$ans = inTrinagle($x2[1], $y2[1], $x2[2], $y2[2], $x2[3], $y2[3], $dot['x'], $dot['y']);
		if (($ans['a'] >= 0 && $ans['b'] >= 0 && $ans['c'] >= 0) || ($ans['a'] <= 0 && $ans['b'] <= 0 && $ans['c'] <= 0)) {
			printScrTriang($ans['a'], $ans['b'], $ans['c'], $dot['x'], $dot['y'], 'Found in triangle #2 !!!111один!1упчяка');
			die;
		} else {
			echo "Dot( x = " . $dot['x'] . ", y = " . $dot['y'] . " )" . "<br>" . "Out of figure!";
			die;
		}
	}
# maybe in square? doing with square
} elseif (($X[1] <= $dot['x'] && $X[2] >= $dot['x']) && ($Y[1] <= $dot['y'] && $Y[1] >= $dot['y'])) {
	# so dot in square
	echo "Dot( x = " . $dot['x'] . ", y = " . $dot['y'] . " )" . "<br>" . "In square!!1!";
	die;
} else echo "Dot( x = " . $dot['x'] . ", y = " . $dot['y'] . " )" . "<br>" . "Out of figure!";
die;

function inTrinagle($x1 = null, $y1 = null, $x2 = null, $y2 = null, $x3 = null, $y3 = null, $dotX = null, $dotY = null ) 
{
	if ($x1 !== null && $x2 !== null && $x3 !== null && $y1 !== null && $y2 !== null && $y3 !== null && $dotX !== null && $dotY !== null) {
		$a = ($x1 - $dotX) * ($y2 - $y1) - ($x2 - $x1) * ($y1 - $dotY);
		$b = ($x2 - $dotX) * ($y3 - $y2) - ($x3 - $x2) * ($y2 - $dotY);
		$c = ($x3 - $dotX) * ($y1 - $y3) - ($x1 - $x3) * ($y3 - $dotY);
	} else {
		return null;
	}
	return ['a' => $a, 'b' => $b, 'c' => $c];
}

function printScrTriang($a = null, $b = null, $c = null, $dotX = null, $dotY = null, $message = '')
{
	echo "Dot( x = " . $dotX . ", y = " . $dotY . " )" . "<br>";
	echo "a = " . $a . "<br>";
	echo "b = " . $b . "<br>";
	echo "c = " . $c . "<br>";
	echo $message;

}