Create find_roots_of_quadratic_equation.php (#7506)

Find roots of quadratic equation in php, comment in the code of what everything does.

Co-authored-by: Kartikeya Saini <111000515+hi-Kartik2004@users.noreply.github.com>

program/find-roots-of-quadratic-equation/find_roots_of_quadratic_equation.php

@@ -0,0 +1,14 @@
+<?php
+// Give the input values for the formula
+$inputA = 5;
+$inputB = 10;
+$inputC = 2;
+
+// $sumD is the part of the equation that is inside of the square root
+$sumD = pow($inputB, 2) - 4 * $inputA * $inputC;
+
+// The rest of the equation. Everything is put in () so it is calculated in the right order.
+$outputPositive = (-$inputB + pow($sumD, 0.5)) / (2 * $inputA);
+$outputNegative = (-$inputB - pow($sumD, 0.5)) / (2 * $inputA);
+
+echo "x = $outputPositive &nbsp; or &nbsp; x = $outputNegative";