Equality case in the Steiner perimeter inequality
= Equality case in the Steiner perimeter inequality
Equality holds exactly when $u_+'=-u_-'$, so the midpoints of all perpendicular chords lie on one line parallel to the symmetrizing axis.
= Equality case in the Steiner perimeter inequality
Equality holds exactly when $u_+'=-u_-'$, so the midpoints of all perpendicular chords lie on one line parallel to the symmetrizing axis.