math
posted by tina on .
(Px – 20) (100 – 2 Px + Pyg)
Differentiating with respect to P we get
100 – 4Px + Pyg + 40 = 0
I don't understand how this is calc... whenever I multiply through and take the deriv I get another answer. Do you first multiply Px through then 20??

Pyg will be treated as a constant.
It doesn'matter how you multiply it out.
Px*1002Px^2+PxPyg2000+40Px+20Pyg=f
1004Px+Pyg+40=0 
How do the 2000 and 20pyg cancel out...the first pyg is still there?