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用JavaScript计算二次函数的根值

阅读：5726 输入：2017-06-03 14:42:29

用JavaScript计算二次函数的根值，体现的JavaScript在网页数学运算方法的优势，这只是一个比较简单的应用。

<title>JavaScript计算二次函数的根值</title>
<SCRIPT>
<!-- Begin
<!--
function findRoots() {
  var ff = document.forms[
"quad"];
  var a = ff.elements[
"a"].value;
  var b = ff.elements[
"b"].value;
  var c = ff.elements[
"c"].value;
  if(a.length == 0 || a == "0") {
    alert("The co-efficient of x^2 must be a non-zero number.");
    return;
  }
  var addOf = -1*b;
  var rootOf = b*b - 4*a*c;
  var denomOf = 2*a;
  ff.elements[
"be"].value = addOf;
  ff.elements[
"root"].value = rootOf;
  ff.elements[
"denom"].value = denomOf;
  var firstDivide = addOf / denomOf;
  if(rootOf == 0) {
    ff.elements[
"x1"].value = firstDivide;
    ff.elements[
"x2"].value = "";
  } else if(rootOf < 0) {

rootOf *= -1;
    rootOf = Math.sqrt(rootOf);
    rootOf /= denomOf;
    ff.elements[
"x1"].value = firstDivide + " + i" + rootOf;
    ff.elements[
"x2"].value = firstDivide + " - i" + rootOf;
  } else if(rootOf > 0) {
    rootOf = Math.sqrt(rootOf);
    rootOf /= denomOf;
    ff.elements[
"x1"].value = (firstDivide + rootOf);
    ff.elements[
"x2"].value = (firstDivide - rootOf);
  }
}

</script>
<form name="quad" onsubmit="return false;">
y = <input name="a" value="6" class="num" size=3>x<sup>2</sup> + 
<input name="b" value="12" class="num" size=3>x + 
<input name="c" value="18" class="num" size=3>
</p><p>
<input type="button" value="计算" onclick="findRoots();">
</p>
<p>
<table cellpadding=0 cellspacing=0 border=0>
<tr>
<td rowspan=3 align="right">
x<sub>1</sub>, x<sub>2</sub> = 
</td>
<td align="center">
<input name="be" class="num" size=2> + root(<input name="root" class="num">)
</td>
<td rowspan=3>
 = 
</td>
<td rowspan=3 align="left">
<input name="x1" class="num" size="25"><br><input name="x2" class="num" size="22">
</td>
</tr>
<tr>
<td>
<hr width="100%" size=1>
</td>
</tr>
<tr>
<td align="center">
<input name="denom" class="num">
</td></tr></table></p>
</form>

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