用JavaScript计算二次函数的根值_计算转换特效

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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。

      <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>x² + <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"> x₁, x₂ = </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>