I decided to go with trigonometric form of a parabola.
3
Expression 4: negative 2cosine left parenthesis, 2arccos left parenthesis, StartFraction, StartRoot, 2 , EndRoot Over 2 , EndFraction left parenthesis, "x" minus 1 , right parenthesis , right parenthesis , right parenthesis minus 1−2cos2arccos22x−1−1