58.6×0.5+58.6÷2-1=58.6×0.5+58.6x0.5-1=58.6×0.5x2-1=58.6×1-1=58.6-1=57.6
58.6×0.5+58.6÷2-1=58.6×05+58.6×0.5-1=58.6×（0.5+0.5）-1=58.6×1-1=57.6
