$a_base = 3;
$b_left_side = 4;
$c_right_side = 5;
$perimeter = $a_base + $b_left_side + $c_right_side;
echo "Perimeter = " . number_format($perimeter, 2, '.', ',') . "<br />";
$semi_perimeter = ($a_base + $b_left_side + $c_right_side) / 2;
$area_triangle1 = sqrt($semi_perimeter * ($semi_perimeter - $a_base) *
($semi_perimeter - $b_left_side) *
($semi_perimeter - $c_right_side));
echo "Area triangle1 = " . number_format($area_triangle1, 2, '.', ',') . "<br />";
$b_base = 4;
$a_right_side = 6;
$angle_ab = 55;
$area_triangle2 = ($a_right_side * $b_base * sin((M_PI / 180) * $angle_ab)) / 2;
echo "Area triangle2 = " . number_format($area_triangle2, 2, '.', ',') . "<br />";
$height = 5;
$b_base = 8;
$area_triangle3 = ($b_base * $height) / 2;
echo "Area triangle3 = " . number_format($area_triangle3, 2, '.', ',') . "<br />";
/*
run:
Perimeter = 12.00
Area triangle1 = 6.00
Area triangle2 = 9.83
Area triangle3 = 20.00
*/
