Question

x(x+1)分之1+(x+1)(x+2)分之1+(x+2)(x+3)分之1 以此类推,最后一个是（x+8）（x+9）分之

Answer 1

=1/x-1/(x+1)+1/(x+1)-1/(x+2)+……+1/(x+8)-1/(x+9)

=1/x-1/(x+9)

=9/(x²+9x)