Try this:
<html>
<head>
<script type="text/javascript">
function calculate(){
var hypo = document.pyform.hypotenuse.value;
var perp = document.pyform.perpendicular.value;
var base = document.pyform.base.value;
if(hypo == "?" || hypo == ""){
calchypo();
} else if(perp == "?" || perp == ""){
calcperp();
} else if(base == "?" || base == ""){
calcbase();
} else {
document.getElementById("result").innerHTML = "";
document.getElementById("pseudo").innerHTML = "";
}
}
function calchypo(){
var perp = document.pyform.perpendicular.value;
var base = document.pyform.base.value;
var resultspace = document.getElementById("result");
var hyp = Math.sqrt(perp*perp + base*base);
resultspace.innerHTML = "h = "+hyp;
document.getElementById("pseudo").innerHTML = "h<sup>2</sup> = p<sup>2</sup> + b<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "h<sup>2</sup> = ("+perp+")<sup>2</sup> + ("+base+")<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "h<sup>2</sup> = "+perp*perp+" + "+base*base+"<br>";
document.getElementById("pseudo").innerHTML += "h<sup>2</sup> = "+parseInt(perp*perp + base*base)+"<br>";
document.getElementById("pseudo").innerHTML += "h = "+Math.sqrt(perp*perp + base*base)+"<br>";
}
function calcperp(){
var hypo = document.pyform.hypotenuse.value;
var base = document.pyform.base.value;
var resultspace = document.getElementById("result");
var perp = Math.sqrt(hypo*hypo - base*base);
resultspace.innerHTML = "p = "+perp;
document.getElementById("pseudo").innerHTML = "p<sup>2</sup> = h<sup>2</sup> - b<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "p<sup>2</sup> = ("+hypo+")<sup>2</sup> - ("+base+")<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "p<sup>2</sup> = "+hypo*hypo+" - "+base*base+"<br>";
document.getElementById("pseudo").innerHTML += "p<sup>2</sup> = "+parseInt(hypo*hypo - base*base)+"<br>";
document.getElementById("pseudo").innerHTML += "p = "+Math.sqrt(hypo*hypo - base*base)+"<br>";
}
function calcbase(){
var hypo = document.pyform.hypotenuse.value;
var perp = document.pyform.perpendicular.value;
var resultspace = document.getElementById("result");
var base = Math.sqrt(hypo*hypo - perp*perp);
resultspace.innerHTML = "b = "+base;
document.getElementById("pseudo").innerHTML = "b<sup>2</sup> = h<sup>2</sup> - p<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "b<sup>2</sup> = ("+hypo+")<sup>2</sup> - ("+perp+")<sup>2</sup><br>";
document.getElementById("pseudo").innerHTML += "b<sup>2</sup> = "+hypo*hypo+" - "+perp*perp+"<br>";
document.getElementById("pseudo").innerHTML += "b<sup>2</sup> = "+parseInt(hypo*hypo - perp*perp)+"<br>";
document.getElementById("pseudo").innerHTML += "b = "+Math.sqrt(hypo*hypo - perp*perp)+"<br>";
}
</script>
<style type="text/css">
input[type=text] {
border: 1px solid #FF9900;
padding: 3px;
color: #B17704;
}
input[type=text]:focus {
background-color: #EEE1C8;
}
body {
font-family: Arial,Verdana,sans-serif,monospace;
}
</style>
</head>
<body>
<form name="pyform">
Hypotenuse(h<sup>2</sup>) : <input type="text" name="hypotenuse">
Perpendicular(p<sup>2</sup>) : <input type="text" name="perpendicular">
Base(b<sup>2</sup>) : <input type="text" name="base">
<input type="button" onclick="calculate();" value="calculate">
</form>
<font color="red">Result:</font>
<br>
<span id="result"></span>
<br>
<font color="red">Synthesis:</font>
<div id="pseudo">
</div>
</body>
</html>