function GeoCalc(){
var Surface;
sidea = eval(document.trapeze.sidea.value);
sideb = eval(document.trapeze.sideb.value);
height = eval(document.trapeze.height.value);

if((sidea > 0) && (sideb > 0) && (height > 0)){

	Surface = FormatNumber((height * (sidea + sideb))/2);
	
	if(Surface >= 100)
		resultSurface = "&#928; = 3.141592653589793<br />Surface<br />" + Surface + "  cm<sup>2</sup><br />" + FormatNumber(Surface/10000) + "  m<sup>2</sup><br />";
	else
		resultSurface = "&#928; = 3.141592653589793<br />Surface<br />" + Surface + "  cm<sup>2</sup><br />";
	
	document.getElementById("surface").innerHTML = resultSurface;
}

}