已知弧长6390,弧高690,求半径和玄长以及圆心角

已知弧长C=6390,弧高H=690,求半径R和玄长L以及圆心角A?
Rn+1=(1-(Rn*COS(C/(2*Rn))-Rn+H)/((C/2)*SIN(C/(2*Rn))-H))*Rn
R0=7397
R1=7275.337
R2=7279.117
R3=7279.121
R4=7279.121
R=7279.121
A=C/R=6390/7279.121=0.877853弧度=0.877853*180/PI=50.297度
L=2*R*SIN(A/2)
=2*7279.121*SIN(50.297/2)
=6186.788