4/3+7/12-9/20+11/30-13/42+15/56简便运算

4/3+7/12-9/20+11/30-13/42+15/56=(1+3)/(1*3)+(3+4)/(3*4)-(4+5)/(4*5)+(5+6)/(5*6)-(6+7)/(6*7)+(7+8)/(7*8)=(1+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)=1+1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+...