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>