Expression 2: Start sum from "n" equals 0 to "k" , end sum, StartFraction, left parenthesis, negative 1 , right parenthesis Superscript, "n" , Baseline "x" Superscript, 2 "n" plus 1 , Baseline Over left parenthesis, 2 "n" plus 1 , right parenthesis ! , EndFractionk∑n=0−1nx2n+12n+1!