Answer
4 terms
Work Step by Step
Recall the Taylor series for $\tan^{-1} x= x-\dfrac{x^3}{3}+\dfrac{ x^5}{5}-....; |x| \leq 1$
Now, $| Error|=(48) |\dfrac{(-1)^{n-1} (\dfrac{1}{18})^{2n-1}}{2n-1}| \lt \dfrac{1}{3}(10^{-6})$
and $48|\dfrac{ (\dfrac{1}{18})^{2n-1}}{2n-1}| \lt \dfrac{1}{3}(10^{-6})$
$\implies n \geq 4$
Thus, the required number of terms are: $4$.