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MCQ
The principal solution of `cos^-1(-1/2)` is :
Options
`pi/3`
`pi/6`
`(2pi)/3`
`(3pi)/2`
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Solution
The principal solution of `cos^-1(-1/2)= ` An angle in [0,π], whose cosine is -1/2
⇒ `cos^-1(-1/2) = pi - "cos"^-1 (1/2)` .....[because cos-1 (-x) = π - cos x]
`= pi - pi/3 = (2pi)/3`
Concept: Inverse Trigonometric Functions - Inverse Trigonometric Functions - Principal Value Branch
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