The length of the major axis of the ellipse below is 13.
Let P be the point on the ellipse
Let F1 and F2 are the two focus
The distance of red line is PF1 and the distance of blue line is PF2
In ellipse, the sum of the distance from point P to the focus is equal to the length of major axis
The sum of PF1 and PF2 = length of major axis
So PF1 + PF2 = 13
The sum of red line and blue line = 13