Converting X Y Z

Hello Everyone. I need some help in converting x y z to lat long . Now i have the formula which is
EarthRadius = 6378.137;
var x = earthRadius * Math.cos(lat)*Math.cos(lon);
var y = earthRadius * Math.cos(lat)*Math.sin(lon);
var z = earthRadius * Math.sin(lat);

But i want it to be like

Lat = ____

Long = ___

Im pretty bad at math please help me.
Example , X = 1 , Y = 2 , Z = 3 .