Pressure derivation If possible, fast please.

[kristiine_c]

Homework Statement

I' have formula P=Po+(mg)/(π*r^2)

I need to derive it.
I have derived it P'(r)=(2mg/π(r^3))*Δr

but it's incorrect. The teacher wrote me "You have forgotten about ΔPo and Δm!"
I don't know how I could derive it. It's for mistake calculation in laborotory work!

 

[gneill]

Homework Statement

I' have formula P=Po+(mg)/(π*r^2)

I need to derive it.
I have derived it P'(r)=(2mg/π(r^3))*Δr

but it's incorrect. The teacher wrote me "You have forgotten about ΔPo and Δm!"
I don't know how I could derive it. It's for mistake calculation in laborotory work!

Your question is without context.