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Prove the following: 3 sin−1 x = sin−1 (3x − 4x3), x∈[-1/2,1/2] - Mathematics

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Question

Prove the following:

3 sin−1 x = sin−1 (3x − 4x3), `x ∈ [-1/2, 1/2]`

Theorem
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Solution

Let x = sin θ

Then, sin−1 x = θ

We have

R.H.S = sin−1 (3x − 4x3) = sin−1 (3 sin θ − 4 sin3θ)

= sin−1 (sin 3θ) = sin−1 (3 sin θ − 4 sin3θ)

= 3θ = sin−1 (3 sin θ − 4 sin3θ)

= 3 sin−1 x = sin−1 (3 sin θ − 4 sin3θ)

R.H.S = L.H.S

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Chapter 2: Inverse Trigonometric Functions - Exercise 2.2 [Page 47]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 2 Inverse Trigonometric Functions
Exercise 2.2 | Q 1 | Page 47

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