弦长L=20,弧长C=40,求半径R?
Rn+1=(1+(L-2*Rn*SIN(C/(2*Rn)))/(L-C*COS(C/(2*Rn))))*Rn
R0=11
R1=10.509
R2=10.551
R3=10.551
R=10.551