Derive equation 5.42 and then show that with proper definitions one can write K = n pfPFNLPTNL k = (v.), (v,) th + ,f + D, B2 , + D,B2 ." + DB2 R, 'a, th 1-2 (5.42) Derive equation 5.42 and then show that with proper definitions one can write K = n pfPFNLPTNL k = (v.), (v,) th + ,f + D, B2 , + D,B2 ." + DB2 R, 'a, th 1-2 (5.42)