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设å弧ABçåå¿è§ä¸º2a(弧度)ï¼å
l=2a*R
a*R=l/2
OD=R*cosa
h=CD=OC-OD=R*(1-cosa)
cosa=1-h/R
cosa*cosa=(1-h/R)^2
AC=a*R
AC^2=CD^2+AD^2
a*a*R*R=h*h+R*R*sina*sina
sina*sina=a^2-h^2/R^2
1=cosa*cosa+sina*sina=(1-h/R)^2+a^2-h^2/R^2=1-2*h/R+a^2
R=a^2/(2h)
R*R*R=(a*R)^2/(2h)=l^2/(8h)=(1.3)^2/(8*0.4)=5.28125
Râ1.7415