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Find the general solution of the following equation: tan3θ = 3 tanθ. - Mathematics and Statistics

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Question

Find the general solution of the following equation: 

tan3θ = 3 tanθ.

Sum

Solution

tan3θ = 3tanθ
∴ tan3θ - 3tanθ = 0
∴ tanθ (tan2θ - 3) = 0
∴ either tanθ = 0 or tan2θ - 3 = 0
∴ either tanθ = 0 or tan2θ = 3
∴ either tanθ = 0 or tan2θ = (√3)2
∴ either tan θ = 0 or tan2θ = `(tan  pi/3)^2    ...[∵ tan  pi/(3) = sqrt(3)]`
∴ either tanθ = 0 or tan2θ = `tan^2  pi/(3)`

The  general solution of 
tanθ = 0 is θ = nπ, n ∈ Z and 
tan2θ = tan2α is θ = nπ ± α, n ∈ Z.

∴ the required general solution is given by
θ = nπ, n ∈ Z or θ = `nπ ± pi/(3)`, n ∈ Z.

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Trigonometric Equations and Their Solutions
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Chapter 3: Trigonometric Functions - Exercise 3.1 [Page 75]

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