For the calculation of critical radius of insulation for a cylindrical tube, which of the following differentiation is correct?

( frac{d( frac{K}{HR_2}+ln( frac{R_2}{R_1}))}{dR_1} ) = 0

( frac{d( frac{K}{HR_1}+ln( frac{R_2}{R_1}))}{dR_2} ) = 0

( frac{d( frac{K}{HR_2}+ln( frac{R_1}{R_2}))}{dR_1} ) = 0

( frac{d( frac{K}{HR_2}+ln( frac{R_2}{R_1}))}{dR_2} ) = 0

For the calculation of critical radius of insulation for a cylindrical

1.	For the calculation of critical radius of insulation for a cylindrical tube, which of the following differentiation is correct?
A.	( frac{d( frac{K}{HR_2}+ln( frac{R_2}{R_1}))}{dR_1} ) = 0
B.	( frac{d( frac{K}{HR_1}+ln( frac{R_2}{R_1}))}{dR_2} ) = 0
C.	( frac{d( frac{K}{HR_2}+ln( frac{R_1}{R_2}))}{dR_1} ) = 0
D.	( frac{d( frac{K}{HR_2}+ln( frac{R_2}{R_1}))}{dR_2} ) = 0
Answer» E.