密语“XYZZY”的数学由来
熟悉 windows 的用户可能知道 xyzzy 是扫雷的秘籍,而 Linux 用户们所知道的更多是它源自于文字界面的 adventure 游戏。
最近我在寻找 adventure 游戏的“攻略”时(见笑了,不过我是真的不大会玩),无意中找到了它的数学来源。
据说这来自于矢量叉乘公式的记忆口诀。
如果
,其中分别是矢量
则有
你看,方程 (1) 各个变量的下标,不正是 吗?然后把方程 (1)的下标两次按照
的变换轮换,就得到 (2) 和 (3) 两个方程了。
不过我们记忆矢量叉乘公式一般是通过行列式来记忆。
2022年8月06日 22:46
Custom Duty is a form of indirect Tax which is applicable on Goods which are imported and exported from India. Any charges applied on the import of goods from another country to India are termed as Import Duty and any charges applied on export of goods from India are termed as Export Duty. Icegate Payment Online The Custom Duty is a combination of these import and export duty which is levied on Goods. This process is common in all counties and as well termed as mandatory on every item. Duty payment charges are based on goods and their dimension along with their official brand price. Thus anyone who intended in the form of import or export of Goods, they should firmly pay the Custom Duty in prior.
2022年8月21日 14:13
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