弧长为周长-2R=2R/3,圆心角(弧度制)为(2R/3)/R=2/3;三角形面积为R^2·sin(1/3)·cos(1/3)= R^2·sin(2/3) /2;则弓形的面积是[R^2·(2/3)/2]-[R^2·sin(2/3) /2]=R^2(1/3-sin(2/3) /2).如果周长为2R+2πR/3的话,最后...