<SCRIPT LANGUAGE="JavaScript">
<!--
var rparti;
var rpart;
var det;
var rparti1;
var rparti2;
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 || a == "") && c != 0) {  
x1 = "error";
x2 = "error";
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;           
rpart = Math.sqrt(det)/(2*a);
rparti = (Math.sqrt(-det)/(2*a))+i;
if (parseFloat(rparti)<0) {
rparti1 = rparti;
rparti2 = (-1*parseFloat(rparti))+i; 
}
else {
rparti1 = (-1*parseFloat(rparti))+i;
rparti2 = rparti;
}
if (rparti1 == "1i") {         
rparti1 = i;
rparti2 = "-i";
}
else if (rparti1 == "-1i") {    
rparti1 = "-i";
rparti2 = 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 = rparti1;
x2 = rparti2;
}
else {                           
x1 = (-b/(2*a)+"+"+rparti1);
x2 = (-b/(2*a)+"+"+rparti2);
}
document.fquad.x1.value=x1;       
document.fquad.x2.value=x2;
}
//-->
</script>

<form name=fquad>
<table align="center">
<tr>
<td>
<input name=fa size=4>
          <font color="black">x<SUP>2</SUP>+</font> 
          <input name=fb size=4>
          <font color="black"> x +</font> 
          <input name=fc size=4>
          <font color="black">= 0</font> 
          <input type=button value="求值" onClick="checkQuad()">
           
          <input type=reset value="重填">
</td>
</tr>
<tr>
<td>
        <h2> <font color="black">x<sub>1</sub>=</font>
<input name=x1 size=35>
<br>
          <font color="black">x<sub>2</sub>=</font>
<input name=x2 size=35>
</h2>
</td>
</tr>
</table>
</form>