（1-1/2²）×（1-1/3²）×（1-1/4²）...省略号乘（1-1/9²）×（1-1/10²)=[(2²-1)(3²-1) (4²-1)(5²-1)(6²-1)(7²-1)(8²-1)(9²-1)(10²-1)]/(2&...