Radio buttons

function ksi1(form) {
var d=parseFloat(form.d.value);
var k1;
form.ans6.value = ((d>0 && d<=15) && (document.form.uc.checked = true))?3.00:
                         ((d>0 && d<=15) && (document.form.lc.checked = true))?1.88:
				 'error';
}

if ((d>0 && d<=15) && (document.form.uc.checked = true))
{
	document.write(k1=3.00);
	}
	else if ((d>0 && d<=15) && (document.form.lc.checked = true))
	{
	document.write(k1=1.88);
	}
		else
	{
		
		document.write(error);
	}
		
<input type="radio" name="radio" id="uc"/>
 <label for="uc">uc </label>
 <input type="radio" name="radio" id="lc"/>
 <label for="uc">uc </label></td>

what am i doing wrong?
so if d is between 0 and 15 and if radio button uc is checked it writes 3.00 and if radio button lc is checked it writes 1.88

Incorrect referencing

// not
document.form.uc.checked
// use
document.form.radio[0].checked
// or
document.getElementById('uc').checked