用JavaScript计算二次函数的根值

2024-09-05 12:22:05

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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 LANGUAGE="JavaScript"><!-- 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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