Just going over partial derivatives and the solution here to question 2 part 3, seems to have a Z rather than a Z squared after the first derivative w.r.t y ?

Is this a mistake or am I missing something? (the latter being most probable).

(Fyy)zz would then be -4/ y cubed or -4 y(power -3)

Should it have been Z(squared)*Y(power -2) instead of ZY(power-2) ?

Graham

[*Corrected – J.P.*]