Question

1/1*2+2/1*2*3+3/1*2*3*4+……+8/1*2*3*4……*9=

Answer 1

（1）由书中知识，+5的相反数是-5，-5的相反数是5，那么数x的相反数是__-x__.数-x的相反数是__x__.数a-b的相反数是__b-a__.数a+b的相反数是__-a-b___.

数a-b的相反数是
把a-b看做x
则相反数是-(a-b)=-a+b=b-a

数a+b的相反数是
把a+b看做x
则相反数是-(a+b)=-a-b

Answer 2

n/(n+1)!
=[(n+1)-1]/(n+1)!
=(n+1)/(n+1)!-1/(n+1)!
=1/n!-1/(n+1)!

所以原式=1/1-1/1*2+1/1*2-1/1*2*3+……+1/1*2*……*8-1/1*2*……*9
=1-1/1*2*……*9
=362879/362880