area of an annular chord section

[timc_fla]

I think my title is self descriptive, it was the best I could come up with.
I haven't seen any examples of this so I can't find the applicable terminology.
Anyway, in the image below I need to find the area of the shaded blue section.
What other measurments do I need to accomplish this?
This is not an annular section.
Any help?

 

[HallsofIvy]

You will need to know either the length of the chord inside the inner circle or the angle those two endpoints make with the center of the circle.

 

[timc_fla]

Okay, I've updated the image, let's assume L is length, what would the formula or formulas be to calculate this?

 

[Ishuda]

Okay, I've updated the image, let's assume L is length, what would the formula or formulas be to calculate this?

Depending on which way you want to go, you may need to determine an angle or segment height as an intermediate step. You might look at
http://www.mathopenref.com/segmentarea.html
or some of the links there to see how you would want to proceed.

 

[timc_fla]

Ok, after much searching I found a formula for this specific problem.
it is at: http://calculus-geometry.hubpages.com/hub/Annulus-Area-Chord-Length-Formula
thank you everyone for you help and suggestions.