Question

How do you simplify `cos(tan^-1 (2/3))`?

Answer 1

`+-3/sqrt 13`

Explanation:

Let `a = tan^(-1)(2/3)`. Tangent is positive in both the first and the

third quadrants.

The given expression is `cos a = +-3/sqrt 13`.

Positive sign for a in the first quadrant and `-` sign for a in the third quadrant..