Expression 19: "R" left parenthesis, "x" , right parenthesis equals "e" Superscript, StartFraction, 10 to the 9th power Over "n" , EndFraction left parenthesis, 1 minus "x" Superscript, negative 10 to the negative 9th power , Baseline , right parenthesis , BaselineRx=e109n1−x−10−9