弧长C=5050,拱高H=675
COS(C/(2R))=(R-H)/R=1-H/R
F(R)=COS(C/(2R))-1+H/R=(R*COS(C/(2R)-R+H)/R
F'(R)=(C/(2R^2))SIN(C/(2R))-H/(R^2)=(C*SIN(C/(2R)-2H)/(2R^2)
Rn+1=[1-(Rn*COS(C/(2Rn))-Rn+H)/((C/2)*(SIN(C/(2Rn))-H)]*Rn
R0=4000
R1=4470.29
R2=4598.15
R3=4605.55
R4=4605.57
半径为：4605.57