Let
A(α,0) and
B(0,β) be the points on the line
5x+7y=50. Let the point
P divide the line segment
AB internally in the ratio
7:3. Let
3x−25=0 be a directrix of the ellipse
E:a2x2+b2y2=1 and the corresponding focus be
S. If from
S, the perpendicular on the
x-axis passes through
P, then the length of the latus rectum of
E is equal to,