= 1/2×( 1- 1/3)+ 1/2×( 1/3- 1/5)+ 1/2×( 1/5- 1/7)+……+ 1/2×( 1/3 1 - 1/33)+ 1/2×( 1/33- 1/35)
= 1/2×( 1- 1/3+ 1/3- 1/5+ 1/5- 1/7+……+ 1/3 1- 1/33+ 1/33- 1/35)
= 1/2×( 1- 1/35)
= 1/2×34/35
= 17/35