sin(∠ACB) = 4/8 = 1/2
therefore ∠ACB = 30°
Therefore since ∠BCO = 90°, ∠ACO = 60°
Therefore ΔOAC is an equilateral triangle because the two radii,
OA and OC are equal, making it isosceles, and it has one 60° angle.
So all the sides of ΔOAC are equal, so OC=8.
So the radius of the wheel is 8, its diameter is 16 and its
area is
pr² = p(8)² = 64p.
Edwin