Question

我向大家数学高手请教个题目,我怎么都做不出来

Answer 1

1/1*4+1/2*5+1/3*6+1/4*7+1/5*8+1/6*9+1/7*10+1/8*11+1/9*12

=1/3{3/1*4+3/2*5+3/3*6+3/4*7+3/5*8+3/6*9+3/7*10+3/8*11+3/9*12}

=1/3{1-1/4+1/2-1/5+1/3-1/6+1/4-1/7……+1/9-1/12}

=1/3{1+1/2+1/3-1/10-1/11-1/12}