The distances a, b, and c, in an ellipse, are related like this
[tex]a^2=b^2+c^2[/tex]
Where 2c is 13, according to the problem.
Let's find c
[tex]\begin{gathered} 2c=13 \\ c=\frac{13}{2}=6.5 \end{gathered}[/tex]
The blue line is equal to a, and the sum of the red and blue lines is 2a.
