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CBSE Class 12 Maths 2010 Solved Paper

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Question : 3 of 29
Marks: +1, -0
What is the principal value of cos−1(−
√3
2
) ?
Solution:  
Let cos−1(−
√3
2
) = x
⇒ cos x = -
√3
2
⇒ cos x = - cos (
π
6
)
⇒ cos x = cos (π−
π
6
)
⇒ cos x = cos (
5π
6
)
⇒ x =
5π
6
Therefore, the principal value of cos−1(−
√3
2
) is
5π
6
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