The formula for the extension in the tapered rod of length l and tapered diametre of $$D_1$$, and $$D_2$$, under the axial tensile load is ............

A

$$\frac{4PL}{\pi ED_1 D_2}$$

B

$$\frac{4PL}{\pi D_1 D_2}$$

C

$$\frac{PL}{\pi ED_1 D_2}$$

D

$$\frac{2PL}{\pi ED_1 D_2}$$