(1+2/5)*(1-2/5)*(1+2/7)*(1-2/7)*.*(1+2/99)*(1-2/99)
=7/5*3/5*9/7*5/7*...*101/99*97/99
=(7/5*9/7*...*101/99)*(3/5*5/7*...*97/99)
=101/5*3/99
=101/165
(1+2/5)*(1-2/5)*(1+2/7)*(1-2/7)*.*(1+2/99)*(1-2/99)
=7/5*3/5*9/7*5/7*...*101/99*97/99
=(7/5*9/7*...*101/99)*(3/5*5/7*...*97/99)
=101/5*3/99
=101/165