Trigonometric substitution.
Restriction on the variable θ of trigonometric function is important. So that the value in radical would not take a negative value. The following expressions can be changed into a trigonometric function. That is called trigonometric substitution.
Trigonometric substitution with sine
Trigonometric substitution with tangent.
Trigonometric substitution with secant.
Another trigonometric substitution with tangent.
