Solved Math problem (ellipse)

Following Problem:

I know:
a; h; b;

I need to know r(h) for the left side of the ellipse ...
Someone can do this?
didn't get this xD

btw:
e = sqrt(a²-r²)
the lenght of the yellow line = const and exact 2*a all the time ...
so u can use it, if u need ...




oh lol ... now i got it

r = sqrt(b² - ((-a + h)² * b²)/a²)

// solved

because of:

x²/a² + y²/b² = 1

EDIT by Moderator: merged posts, please use the edit button instead of double posting.