Question

Find an expression in terms of x, tan(arccos(3x)). Thanks.

Answer 1

and then the pythagorean thm ?

Answer 2

need the third side, which your find via pythagoras
it is
\[\sqrt{1^2-(3x)^2}=\sqrt{1-9x^2}\]

Answer 3

then tangent is "opposite over adjacent" and you are done

Answer 4

it can also be negative right?