1/3×5+1/5×7+1/7×9+···+1/21×23
=1/2×（1/3-1/5+1/5-1/7+……+1/21-1/23）
=1/2×（1/3-1/23）
=1/2×20/69
=10/69是1/3×5+1/5×7+1/7×9+···+1/21×23，你是不是看错了是啊，你看看，我算的就是1/3×5+1/5×7+1/7×9+···+1/21×23=1/2×（1/3-1/5+1/5-1/7+……+1/21-1/23）=1/2×（1/3-1/23）=1/2×20/69=10/69