弧长C=3.5M,拱高H=0.7M,求弦长?
弧半径为R
Rn+1=(1-(Rn*COS(C/(2*Rn))-Rn+H)/((C/2)*SIN(C/(2*Rn))-H))*Rn
R0=2
R1=2.056
R2=2.059
R3=2.059
R=2.059M
弦长=2*(R^2-(R-H)^2)^0.5=3.094M