Original formula = log2 (a1a2 ... a9a10) = log2 (4 5) =10.

T8: Let |F 1F2|=2c.

If the waist length of the isosceles right triangle AF 1F2 is √2 *c and the midpoint m of AF 1 is on the ellipse, then MF 1+MF2=2a.

AF 1=√2 *c/2，

Calculate MF2=√ 10 *c/2 by cosine theorem in triangle MF 1F2.

2a=(√2 +√ 10)*c/2

e=2c/2a=(√ 10 -√2 )/2

Choose c for both.