clear all
y=(a/2)^2/b/4
l=f*(b-y)+z*(a-f)
m=2*(b-y)-a+f
n=2*(b-y)+a-f
o=l*(1/m-1/n)/2
elim l m n y
simp
copy
f
simp symb
6
deri z
f
simp symb
simp symb