(1) S=12r2θS = \frac{1}{2}r^2\thetaS=21r2θ S′=12⋅2r⋅θ=rθS' = \frac{1}{2}\cdot 2r \cdot \theta = r\thetaS′=21⋅2r⋅θ=rθ (2) V=13πr2hV = \frac{1}{3}\pi r^2 hV=31πr2h V′=13πr2=13πr2V' = \frac{1}{3}\pi r^2 = \frac{1}{3}\pi r^2V′=31πr2=31πr2 (3) v=Q2πR2v = \frac{Q}{2\pi R^2}v=2πR2Q v′=12πR2v' = \frac{1}{2\pi R^2}v′=2πR21 (4) u=U(1−r2R2)=U−Ur2R2u = U\left(1 - \frac{r^2}{R^2}\right) = U - U\frac{r^2}{R^2}u=U(1−R2r2)=U−UR2r2 u′=−U2rR2=−2UrR2u' = -U\frac{2r}{R^2} = -\frac{2Ur}{R^2}u′=−UR22r=−R22Ur