求解题过程,懂的不懂的都来看看答案怎么得来的
1/3+1/15+1/35+1/63+1/99
=1/(1x3)+1/(3x5)+1/(5x7)+1/(7x9)+1/(9x11)
=(1-1/11)x(1/2)
=5/11
知道过程的请说明第2步怎么得来的,要过程,谢谢!