In 1738, Daniel, trying to solve a problem in probability theory and the theory of gambling by use of the calculus, stumbled on the concept of the law of diminishing marginal utility of money.
For if these increases of income or utility are reduced to being infinitesimal, one can use both the symbolism and the powerful manipulations of the differential calculus.
因为，如果这些收入或效用的增加可以化为无穷小，那我们既能使用符号表示，也能利用微分学强大的操作了。
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The mystique of the modern calculusutility partly caused by the mathematics itself is essentially the result of the change of the cultural system.