What is tan inverse multiplied by (10/5)

I think you want to know this :

tan^-1 (10/5)  =  about 63.43°

{Note....we aren't  "multiplying" the tangent inverse by 10/5, we're just finding the angle that has a tangent value of 10/5.......don't get confused, here }

It is not What is tan inverse multiplied by (10/5)

It is  tan inverse of (10/5)

this can be written as 

$$tan^{-1}(2)\qquad or \qquad atan(2)$$

The brackets are not always necessary :)