In figure 1, l is the arc length, h is the distance from the arc to the chord, b is the chord length, r is the radius of the circle where the bow is located, and α (/'? What if? /) is the central angle.

α=l/r radian =(l/r)*( 180/PI) degrees.

b=2*r*SIN(α/2)

α= 2 * Arcsine ((b/2)/r)= 2 * Arcsine ((r-h)/r)

h=r-r*COS(α/2)

S=PI*r^2*α/360-b*(r-h)/2

If, as shown in Figure 2, only the radius r= 12cm and the distance between the arc and the chord h=6cm are told, how to calculate the area of the light blue part?

α = 2 * arccos ((r-h)/r) = 2 * arccos ((12-6)/12) =120 degrees.

b = 2 * r * SIN(α/2)= 2 * 12 * SIN( 120/2)= 20.785

s=pi*r^2*α/360-b*(r-h)/2=pi* 12^2* 120/360-20.785*( 12-6)/2=88.443