Question

1*1/3+1/3*5+1/5*7+……+1/17*19+1/19*21要过程啊!

Answer 1

1*1/3+1/3*5+1/5*7+……+1/17*19+1/19*21

=1/2×(1-1/3 +1/3-1/5 +1/5-1/7 +...+...+1/17-1/19 +1/19-1/21)

=1/2×(1 - 1/21)

=1/2×20/21

=10/21