Expression 4: "y" equals negative StartFraction, "b" Over 2 , EndFraction left parenthesis, "e" Superscript, StartFraction, "x" Over "b" , EndFraction , Baseline plus "e" Superscript, negative StartFraction, "x" Over "b" , EndFraction , Baseline , right parenthesis plus "b"y=−b2exb+e−xb+b