Trigonometry Manipulation

Geometry Level 2

If tan x + cot x = 12 \tan x + \cot x = 12 , solve for the value of sin 2 x \sin 2x .

1 1/6 1/24 1/12 None 1/3 0

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2 solutions

Nathan Laurence
Nov 21, 2016

s i n x c o s x \frac{sin x}{cos x} + c o s x s i n x \frac{cos x}{sin x} = s i n 2 x + c o s 2 x s i n x c o s x \frac{sin^2x + cos^2x}{sinxcosx} = 1 s i n x c o s x = 12 \frac{1}{sinxcosx} = 12 ; s i n x c o s x sinxcosx = 1 12 \frac{1}{12} ; (Note : s i n 2 x = 2 s i n x c o s x sin 2x = 2sinxcosx ) -> 2 s i n x c o s x = 1 / 6 2sinxcosx = 1/6 -> s i n 2 x = 1 / 6 sin2x = 1/6 . Thus the answer is 1/6

Chew-Seong Cheong
Nov 22, 2016

Relevant wiki: Half Angle Tangent Substitution

By Weierstrass substitution or tangent half-angle substitution, we have:

sin 2 x = 2 tan x 1 + tan 2 x Divide up and down of the RHS by tan x = 2 cot x + tan x = 2 12 = 1 6 \begin{aligned} \sin 2x & = \frac {2\tan x}{1+\tan^2 x} & \small \color{#3D99F6} \text{Divide up and down of the RHS by } \tan x \\ & = \frac 2 {\cot x+\tan x} \\ & = \frac 2{12} = \boxed{\dfrac 16} \end{aligned}

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