Hello NaplesYou've done all the hard work! It's simply that the original expression, , is written as a positive square root. Hence it becomes the positive square root of , which is written as an absolute value: , so that when would make negative, it still gives the corresponding positive value.

Let . Then we shall need to find .2.

Write tan(arc cos(x/3)) in algebraic form

I don't remember how to do this at all, so detailed explanation on what to do would be extremely helpful.

Any help is greatly appreciated.

Grandad