數學表達，更複雜，更一般。比方說牛頓力學，二階導數，就用了加速度。他說方程裏要加時間空間的混合導數。這些二階導數，

來源: 蔣聞銘於 2024-11-07 13:07:20 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

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