Expression 1: "y" equals Start sum from "k" equals 0 to "a" , end sum, StartFraction, 4 Over pi , EndFraction left parenthesis, StartFraction, 1 Over 2 "k" plus 1 , EndFraction sin left parenthesis, left parenthesis, 2 "k" plus 1 , right parenthesis pi "x" , right parenthesis , right parenthesis Has graph. To audio trace, press ALT+T.y=a∑k=04π12k+1sin2k+1πx