geodesy - Get lat/long given current point, distance and bearing

While searching the web, I've encountered the following formulas for calculating the destination point P2's location given the source point P1 = (lat1,long1), the distance from it & the bearing:

lat2 = math.asin( math.sin(lat1)*math.cos(d/R) +
   math.cos(lat1)*math.sin(d/R)*math.cos(brng))

lon2 = lon1 + math.atan2(math.sin(brng)*math.sin(d/R)*math.cos(lat1),
   math.cos(d/R)-math.sin(lat1)*math.sin(lat2))

Where P2=(lat2,lon2).

I was trying to develop the math behind it but could not really get it right

Can someone please show me how to develop the lat2 & lon2 mathematically?