index.js

function insert(num) {
  document.form.textview.value = document.form.textview.value + num;
}

function equal() {
  var exp = document.form.textview.value;
  if (exp) {
    document.form.textview.value = eval(exp);
  }
}

function c() {
  document.form.textview.value = "";
}

function back() {
  var exp = document.form.textview.value;
  document.form.textview.value = exp.substring(0, exp.length - 1);
}

function sin(){
  document.form.textview.value=Math.sin(document.form.textview.value);
}

function cos(){
  document.form.textview.value=Math.cos(document.form.textview.value);
}
function tan(){
  document.form.textview.value=Math.tan(document.form.textview.value);
}
function square(){
	document.form.textview.value = Math.pow(document.form.textview.value, 2);
	}

	function cubed(){
	document.form.textview.value = Math.pow(document.form.textview.value, 3);
	}

	function sqrt2(){
	document.form.textview.value = Math.pow(document.form.textview.value, 1/2);
	}

	function sqrt3(){
	document.form.textview.value = Math.pow(document.form.textview.value, 1/3);
	}