{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算

{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算
{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算

{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算
{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}
=-1/11+1/12-1/12+1/13-1/13+1/14-1/14+1/15
=-1/11+1/15
=-4/165

{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}
第一项与第四项、第三项与第六项 第五项与第八项 可想到抵消，剩下第二项及第七项

=-1/11+1/15 通分 最简公分母是165
=-15/165+11/165
=-4/165