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

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Answer 1 · 2016-05-13T05:41:45

$+-3/sqrt 13$

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..

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