Question

The value of $\cos \left(2Co{s}^{-1}0.8\right)$ is

• A. $0.48$
• B. $0.96$
• C. $0.6$
• D. $0.28$

Answer 1

Answer: (D)

$0.28$

We have,

$\cos \left(2{\cos }^{-1}0.8\right)$

Since,

$2{\cos }^{-1}x={\cos }^{-1}(2x^2-1)$

Therefore,

$=\cos \left({\cos }^{-1}(2\times {\left(0.8\right)}^2-1)\right)$

$=2\times 0.64-1$

$=1.28-1$

$=0.28$

Hence, this is the answer.