## Example 7.2.4(d): Applying the Substitution Rule

This will be a relief because it is easy:*tan(x) = sin(x)/cos(x)*so that the top function is the derivative of the bottom function (except for a minus sign).

Therefore we can apply a previous example (or make the substitution
*u = cos(x)*) to determine the answer right away:

To findtan(x) dx= -ln(cos(x))

*cot(x) dx*is left as an (easy) exercise.