叉积
study from:
https://blog.csdn.net/Puppet__/article/details/76227045
https://www.cnblogs.com/xiexinxinlove/p/3708147.html
https://www.cnblogs.com/aiguona/p/7248311.html
study from:
https://blog.csdn.net/Puppet__/article/details/76227045
https://www.cnblogs.com/xiexinxinlove/p/3708147.html
https://www.cnblogs.com/aiguona/p/7248311.html