A differential arithmetic is proposed for simplifying the observational equation as well as for avoiding the computation of the unknown integer constant.

提出相邻历元间差分算法，大大简化了观测方程，同时避免积分常量的计算。

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Over 1200 videos lessons covering everything from basic arithmetic and algebra to differential equations, physics, chemistry, biology and finance.

可汉学院（Khan Academy） - 超过1200个视频教程，内容涵盖自基础算术、代数至微分方程、物理学、化学、生物学和金融学。

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My friend and I did some arithmetic, some algebra, derived the general formula for the differential at a point-all stuff he had had in the course.

我和我的朋友做了些算术和代数，得到了某一点的微分公式——这些都是他上课学过的。

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