Expression 3: left parenthesis, "y" minus "f" left parenthesis, "A" plus StartFraction, "x" Subscript, 1 , Baseline Over "B" , EndFraction , right parenthesis , right parenthesis equals "f" prime left parenthesis, "A" plus StartFraction, "x" Subscript, 1 , Baseline Over "B" , EndFraction , right parenthesis left parenthesis, "x" minus left parenthesis, "A" plus StartFraction, "x" Subscript, 1 , Baseline Over "B" , EndFraction , right parenthesis , right parenthesisy−fA+x1B=f′A+x1Bx−A+x1B