Expression 2: "y" equals Start sum from "n" equals 0 to "a" , end sum, StartFraction, left parenthesis, negative 1 , right parenthesis Superscript, left parenthesis, "n" , right parenthesis , Baseline "x" Superscript, 2 "n" , Baseline Over left parenthesis, 2 "n" , right parenthesis ! , EndFraction Has graph. To audio trace, press ALT+T.y=a∑n=0−1nx2n2n!