Trigonometry Problem

Geometry Level 2

tan 20 0 ( cot 1 0 tan 1 0 ) = ? \large \tan 200^\circ \left(\cot 10^\circ - \tan 10^\circ \right) = \ ?


The answer is 2.

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1 solution

Chew-Seong Cheong
May 24, 2017

x = tan 20 0 ( cot 1 0 tan 1 0 ) tan ( 18 0 x ) = tan x = tan ( 2 0 ) ( 1 tan 1 0 tan 1 0 ) tan ( x ) = tan x = tan 2 0 ( 1 tan 2 1 0 tan 1 0 ) = 2 tan 2 0 ( 1 tan 2 1 0 2 tan 1 0 ) tan 2 x = 2 tan x 1 tan 2 x = 2 tan 2 0 ( 1 tan 2 0 ) = 2 \begin{aligned} x & = {\color{#3D99F6}\tan 200^\circ} \left(\cot 10^\circ - \tan 10^\circ \right) & \small \color{#3D99F6} \tan (180^\circ - x) = - \tan x \\ & = {-\color{#3D99F6}\tan (-20^\circ)} \left(\frac 1{\tan10^\circ} - \tan 10^\circ \right) & \small \color{#3D99F6} \tan (- x) = - \tan x \\ & = \tan 20^\circ \left(\frac {1-\tan^2 10^\circ}{\tan 10^\circ} \right) \\ & = {\color{#3D99F6}2}\tan 20^\circ \left(\frac {1-\tan^2 10^\circ}{{\color{#3D99F6}2}\tan 10^\circ} \right) & \small \color{#3D99F6} \tan 2x = \frac {2\tan x}{1-\tan^2 x} \\ & = 2\tan 20^\circ \left(\frac 1{\tan 20^\circ} \right) \\ & = \boxed{2} \end{aligned}

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