I'm going to guess what your problem is. I'll bet there are two concentric
circles, the smaller circle has a radius of OP = 6 cm. Chord AB is tangent to
the smaller circle at P. And AB = cm. Find the area of the
shaded region, the shaded segment of the larger circle. Isn't that what
you want?
Draw the two radii OA and OB of the larger circle (in red):
Use the Pythagorean theorem on right triangle OPA.
= radius of larger circle.
Triangle OPA is a 30-60-90 right triangle because its shortest side OP=6 cm
and its longest side OA, is 12, twice the shortest side.
So angle AOP = 60o = π/3 radians, and angle AOB = 120o = 2π/3 radians.
We find the area of the sector OAB and subtract the area of triangle OAB.
Area of the sector is
Area of triangle AOP =
Area of triangle AOB = twice area of AOP =
Subtract the area of the triangle from the area of the sector:
About 88.4 cm2.
Edwin