Calculadora em JavaScript

<!DOCTYPE html>
<html lang="pt-br">
<head>
    <title>Bhaskara</title>
    <meta charset="uft-8">
    <link rel="stylesheet" href="css/style.css" type="text/css">
    <link href="https://fonts.googleapis.com/css?family=Francois+One" rel="stylesheet">
</head>
<body>
    <div class="meio">
        <h1>Calculadora</h1>
        <form name="form1" onsubmit="return false" method="post">
        <label>a=</label>
        <input type="number" name="valA" class="cx_txt"><br>
        <label>b=</label>
        <input type="number" name="valB" class="cx_txt"><br>
        <label>c=</label>
        <input type="number" name="valC" class="cx_txt"><br>
        <p>Resposta:</p>
        <label>Delta=</label>
        <input type="text" name="valD" class="cx_txt"><br>
        <label>x¹=</label>
        <input type="text" name="valX1" class="cx_txt"><br>
        <label>x²=</label>
        <input type="text" name="valX2" class="cx_txt"><br>
        <label>Ápice=</label>
        <input type="text" name="valAP" class="cx_txt"><br>
        <label>y=</label>
        <input type="text" name="valY" class="cx_txt"><br>
        <button class="" onclick='cal()'>Calcular</button>
        <input type="reset" class="btn" value="Limpar">
        </form>
    </div>
    <script type="text/javascript">
        function cal() {
            var a = parseFloat(document.form1.valA.value);
            var b = parseFloat(document.form1.valB.value);
            var c = parseFloat(document.form1.valC.value);

            d = (c * a * 4) - (b * b);
            document.form1.valD.value = d;
            var d = parseFloat(document.form1.valD.value);

            x1 = ([d/d])/(2 * a * c)
            document.form1.valX1.value = x1;
        }
    </script>
 </body>
</html>