Question

How do you find the exact value of cos [tan-1 (-2/3)]?

Answer 1

`cos(tan^(-1)(-2/3)) = 3/sqrt(13)`

Explanation:

If `theta = tan^(-1)(-2/3)`
then we have the situation pictured below:

The hypotenuse is derived using the Pythagorean Theorem
and
The cos can be read directly from the diagram.