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

May 13, 2016

$\pm \frac{3}{\sqrt{13}}$

#### Explanation:

Let $a = {\tan}^{- 1} \left(\frac{2}{3}\right)$. Tangent is positive in both the first and the

The given expression is $\cos a = \pm \frac{3}{\sqrt{13}}$.
Positive sign for a in the first quadrant and $-$ sign for a in the third quadrant..