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If 2 tan-1(cos x) = tan-1(2 cosec x), then find the value of x.

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Question

If 2 tan-1(cos x) = tan-1(2 cosec x), then find the value of x.

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Solution

2 tan-1(cos x) = tan-1(2 cosec x)

∴ `tan^-1 [(2 cos "x")/(1 - cos^2"x")] = tan^-1 (2  "cosec x")     ...[because 2 tan^-1 "x" = tan^-1 ("2x"/(1 - "x"^2))]`

∴ `(2 "cos x")/(1 - cos^2 "x") = 2  "cosec  x"`

∴ `(2 "cos x")/(sin^2 "x") = 2/ "sin  x"`

∴ cos x = sin x

∴ x = `pi/4`        ....`[because sin  pi/4 = cos  pi/4]`

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Chapter 3: Trigonometric Functions - Miscellaneous exercise 3 [Page 110]

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Balbharati Mathematics and Statistics 1 (Arts and Science) [English] Standard 12 Maharashtra State Board
Chapter 3 Trigonometric Functions
Miscellaneous exercise 3 | Q 26 | Page 110

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