l（are length)=弧长 n=圆心角r（radius）=半径C（circumstances）=圆的周长π=圆周率 π读作“pai” ,近似等于3.14,即π≈3.14l= 4πcm n = 60°根据l = (n×π×r) ÷ 180推算出 r = (180×l )÷(n×π)= ( 180×4...