Mathematics

Problem

For the identity

\tan 2\theta = \dfrac{2\tan\theta}{1-\tan^2\theta}

to be defined, which of the following conditions on

\tan\theta

must hold? a)

\tan\theta \neq 0

|\tan\theta|<1

\tan\theta \neq \pm 1

\tan\theta \neq \pm\sqrt{3}