已知弦长L=200,弧长C=210,求半径R
Rn+1=(1+(L-2*Rn*SIN(C/(2*Rn)))/(L-C*COS(C/(2*Rn))))*Rn
R0=200
R1=194.692
R2=195.017
R3=195.018
R4=195.018
R=195.018