1.10: Substitution
( \newcommand{\kernel}{\mathrm{null}\,}\)
More complicated functions can be integrated using the chain rule. Since ddxf(g(x))=f′(g(x))⋅g′(x),
we have ∫f′(g(x))⋅g′(x)dx=f(g(x))+c.
This integration formula is usually implemented by letting y=g(x). Then one writes dy=g′(x)dx to obtain ∫f′(g(x))g′(x)dx=∫f′(y)dy=f(y)+c=f(g(x))+c.