要完成此效果需要两个步骤
第一步：把如下代码加入到<head>区域中
<SCRIPT LANGUAGE="JavaScript">
<!-- Begin
var rootparti;
var rootpart;
var det;
var rootparti1;
var rootparti2;
var a;
var b;
var c;
var x1;
var x2;
var i = "i";
function checkQuad() {
var a = document.fquad.fa.value;
var b = document.fquad.fb.value;
var c = document.fquad.fc.value;
if (a == 0 && c != 0) {
x1 = -c / b;
x2 = "Not a quadratic equation, but here is your answer for x";
document.fquad.x1.value=x1;
document.fquad.x2.value=x2;
}
else if (a == "" && c != 0) {
x1 = -c / b;
x2 = "Not a quadratic equation";
document.fquad.x1.value=x1;
document.fquad.x2.value=x2;
}
else {
quad();
}
}
function quad() {
var a = document.fquad.fa.value;
var b = document.fquad.fb.value;
var c = document.fquad.fc.value;
det = Math.pow(b,2) - 4 * a * c;
rootpart = Math.sqrt(det) / (2 * a);
rootparti = (Math.sqrt(-det) / (2 * a)) + i;
if (parseFloat(rootparti) < 0) {
rootparti1 = rootparti;
rootparti2 = (-1 * parseFloat(rootparti)) + i;
}
else {
rootparti1 = (-1 * parseFloat(rootparti)) + i;
rootparti2 = rootparti;
}
if (rootparti1 == "1i") {
rootparti1 = i;
rootparti2 = "-i";
}
else if (rootparti1 == "-1i") {
rootparti1 = "-i";
rootparti2 = i;
}
if (det == 0) {
x1 = x2 = -b / (2 * a);
}
else if (det > 0) {
x1 = (-b + Math.sqrt(det)) / (2 * a);
x2 = (-b - Math.sqrt(det)) / (2 * a);
}
else if ((-b / (2 * a)) == 0) {
x1 = rootparti1;
x2 = rootparti2;
}
else {
x1 = (-b / (2 * a) + " + " + rootparti1);
x2 = (-b / (2 * a) + " + " + rootparti2);
}
document.fquad.x1.value=x1;
document.fquad.x2.value=x2;
}
// End -->
</script>
第二步：把如下代码加入到<body>区域中
<form name=fquad>
<table align="center">
<tr>
<td>
<h2>
<input name=fa size=4>
<font color="#33FF33">x<SUP>2</SUP>+</font>
<input name=fb size=4>
<font color="#33FF33"> x +</font>
<input name=fc size=4>
<font color="#33FF33">= 0</font>
<input type=button value="求值" onClick="checkQuad()">
<input type=reset value="重填">
</h2>
</td>
</tr>
<tr>
<td>
<h2> <font color="#33FF33">x<sub>1</sub>=</font>
<input name=x1 size=45>
<br>
<font color="#33FF33">x<sub>2</sub>= </font>
<input name=x2 size=45>
</h2>
</td>
</tr>
</table>
</form>
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