知弧长C、弦长L,弧高H,求弧半径R?
知L和H：R=H/2+L^2/(8*H)
知C和L：Rn+1=(1+(L-2*Rn*SIN(C/(2*Rn)))/(L-C*COS(C/(2*Rn))))*Rn
知C和H：Rn+1=(1-(Rn*COS(C/(2*Rn))-Rn+H)/((C/2)*SIN(C/(2*Rn))-H))*Rn