<script>
function vypln(){
i1 = document.getElementById('jedna').value
i2 = document.getElementById('dva').value
i3 = document.getElementById('tri').value

if (document.getElementById('rad1').checked
document.getElementById('ta').value = "bla"+i1+"bla"+i2
} else {
document.getElementById('ta').value = "bla"+str(int(i1) + int(i2))+"bla"+i3
}
</script>
<input id="jedna" />
<input id="dva" />
<input id="tri" />
<input name="rad" value=1 id=rad1><input name="rad" value=1 id=rad2>
<textarea id=ta></textarea>
<input type+button onclick="vypln()">
</script>

if ($volba=="volba1") {
echo ("blabla".$pole1."blabla".$pole2."blabla".$pole3."blabla") 
} else {
echo ("bloblo".(intval($pole1)+intval($pole2))."bloblo".$pole3."bloblo") 
}