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Find the value of the following: tan-1(1)+cos-1(-12)+sin-1(-12) - Mathematics

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Question

Find the value of the following:

`tan^(-1)(1) + cos^(-1) (-1/2) + sin^(-1) (-1/2)`

Sum

Solution 1

Let `tan^(-1) (1)` = x Then tan x= 1 = tan `pi/4`

`:. tan^(-1) (1) = pi/4`

Let `cos^(-1) (-1/2) =  y` Then, `cos y = -1/2 = -cos(pi/3) = cos(pi - pi/3) = cos ((2pi)/3)`

`:. cos^(-1) (- 1/2) = (2pi)/3`

Let `sin^(-1) (-1/2) = z`. Then `sin z =-1/2 = -sin(pi/6) = sin(-pi/6)`

`:. sin^(-1)(-1/2) = - pi/6`

`:. tan^(-1) (1) + cos^(-1) (-1/2) + sin^(-1) (-1/2)`

`= pi/4 + (2pi)/3 - pi/6`

`= (3pi + 8pi - 2pi)/12 `

`= (9pi)/12 = (3pi)/4`

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Solution 2

`"tan"^-1 (1) + "cos"^-1 (-1/2) + "sin"^-1 (-1/2)`

`= "tan"^-1 ("tan" pi/4) + "cos"^-1 ("cos" (2pi)/3) + "sin"^-1 "sin" ((-pi)/6)`

`= pi/4 + (2pi)/3 + ((-pi)/6)`

`= (3pi + 8pi - 2pi)/12`

`= (9 pi)/12 = (3 pi)/4`

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Chapter 2: Inverse Trigonometric Functions - Exercise 2.1 [Page 42]

APPEARS IN

NCERT Mathematics [English] Class 12
Chapter 2 Inverse Trigonometric Functions
Exercise 2.1 | Q 10 | Page 42

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