15/2/(1-(5+3))=15/2/(-7)=-(15/14)15/2除以(1减(5/1加3/1))简便方法计算急急急急急急急急急急急5/1=53/1=33+5=81-8=-715/2/(-7)=15/2*(-7)=15/(-14)=-(15/14)