MathPHP\Functions\ArithmeticTest::testProduct PHP Метод

    public function testProduct()
    {
        // f(x) = x² + 8x - 12
        $f = function ($x) {
            return $x ** 2 + 8 * $x - 12;
        };
        // g(x) = x - 9
        $g = function ($x) {
            return $x - 9;
        };
        // Π(x) = f(x) * g(x) = x³ - x² -84x + 108
        $product = Arithmetic::multiply($f, $g);
        // Π(0) = 108
        $expected = 108;
        $x = $product(0);
        $this->assertEquals($expected, $x);
        // Π(5) = -212
        $expected = -212;
        $x = $product(5);
        $this->assertEquals($expected, $x);
        // Π(-5) = 378
        $expected = 378;
        $x = $product(-5);
        $this->assertEquals($expected, $x);
        // Π(100) = 981708
        $expected = 981708;
        $x = $product(100);
        $this->assertEquals($expected, $x);
        // Π(-100) = -1001492
        $expected = -1001492;
        $x = $product(-100);
        $this->assertEquals($expected, $x);
    }