Question

2分之一乘3分之一加3分之一乘4分之一.加8分之一乘9分之一,用简便方法计算

Answer 1

1/2*1/3+1/3*1/4+1/4*1/5+1/5*1/6+1/6*1/7+1/7*1/8+1/8*1/9
=1/3(1/2+1/4)+1/5(1/4+1/6)+1/7(1/6+1/8)+1/8*1/9
=1/4+1/12+1/24+1/72
=1/4(1+1/3)+1/24(1+1/3)
=1/3+1/3*1/6=1/3*(1+1/6)=7/18