已知弧形的弧长16800,弦长（ 就是那个直线）16160,求面积 ,

已知弧形的弧长C=16800,弦长(就是那个直线)L=16160,求面积S?
弧半径为R,弧所对的圆心角为A.
Rn+1=(1+(L-2*Rn*SIN(C/(2*Rn)))/(L-C*COS(C/(2*Rn))))*Rn
R0=17000
R1=17438.55
R2=17468.43
R3=17468.56
R4=17468.56
R=17468.56
A=C/R
=16800/17468.56
=0.961728弧度
=0.961728*180/PI
=55.1度
S=PI*R^2*A/360-(L/2)*R*COS(A/2)
=PI*17468.56^2*55.1/360-(16160/2)*17468.56*COS(55.1/2)
=21586985.25