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The value of cos (2Cos^-1 0.8) is...

The value of `cos (2Cos^-1 0.8)` is

A

0.81

B

0.56

C

0.48

D

0.28

Text Solution

Verified by Experts

The correct Answer is:
D
We know that
`2 cos^(-1) x = cos^(-1)(2x^(2)-1)`
here, x = 0.8
`therefore 2 cos^(-1)(0.8) = cos^(-1)(2(0.8)^(2)-1)=cos^(-1)(0.28)`
Now, `cos(cos^(-1)(x))=x`.
`therefore cos(cos^(-1)(0.28))=0.28`
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