Desmos needs to know the area to the left of the critical value (Zc) we're trying to find. Since the middle area is equal to the confidence level, the area to the left of Zc = (1+c)/2.
Critical Value, Zc, is:
4
Expression 5: "z" Subscript, "c" , Baseline equals "X" .inversecdf left parenthesis, StartFraction, 1 plus "c" Over 2 , EndFraction , right parenthesis equals 1.9 5 9 9 6 3 9 8 4 5 4zc=X.inversecdf1+c2