规律：1/(a*b)=[1/(b-a)]*(1/a-1/b)1.1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=1/2+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)=1/2+1/2-1/3+1/3-1/4+...+1/8-1/9+1/9+1/10（中间项都对...
规律：1/(a*b)=[1/(b-a)]*(1/a-1/b)1.1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=1/2+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)=1/2+1/2-1/3+1/3-1/4+...+1/8-1/9+1/9+1/10（中间项都对...