Right, what we are going to do is let's say that Y equals er total product  labour X equals labour U, right, equals sorry Y is the average product  let Y equal the average product of labour X labour input, U equals total product of labour, right, V er equals  L as well Okay,, right, so  differentiating the average product curve and average product function in respect to labour , alright, we get L times D T P right, by D L minus  Q P L all over L squared  .