Question

tanx + tan2x / 1 - tanxtan2x = 4

(Using the arctan formula)

Answer 1

$tan(a + b) = \frac{tana + tanb}{1 - tana \times tanb} \\ \frac{tanx + tan2x}{1 - tanx \times tan2x} = 4 \\ tan(x + 2x) = 4 \\ tan3x = 4 \\ x = \frac{1}{3} {tan}^{ - 1} 4$