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Pure · Integration

Chapter 1 · 4

The idea

The constant of integration

Why every indefinite integral carries a "+C", what that constant actually represents, and how extra information (a point on the curve, an initial condition) pins it down.

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Pure · Integration

The constant of integration

Why every indefinite integral carries a "+C", what that constant actually represents, and how extra information (a point on the curve, an initial condition) pins it down.

Why it works

Differentiation destroys information

The functions x2x^2, x2+5x^2 + 5 and x2−100x^2 - 100 all have exactly the same derivative, 2x2x — differentiating wipes out any constant term, because a constant changes nothing about the slope of a graph.

A family of curves

Integration is the reverse of differentiation. So when you ask "what function has derivative 2x2x?", the honest answer is: a whole family of functions — x2+Cx^2 + C for any constant CC. You cannot know which member of the family is "the" answer from the derivative alone, because the derivative never contained that information in the first place.

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