When a variable x tends to a value a more and more, the process of this trend goes on endlessly, and the difference between x and a tends to zero infinitely, so a is the limit of X.
This difference, called "infinitesimal", is a process of getting smaller and smaller, a process of infinitely approaching zero, and it is not a small number, but a process of approaching zero.
Extended data:
Pay attention to the geometric meaning of differentiation: let Δ x be the increment of point m on the curve on the abscissa y = f(x), Δ y be the increment of the curve on point m corresponding to Δ x on the ordinate, and dy be the increment of the tangent of the curve on point m corresponding to Δ x on the ordinate. F'(x0) is the slope of the tangent of the curve y=f(x) at the tangent point M(x0, f(x0)).
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