Question

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

• A. 0.48
• B. 0.96
• C. 0.6
• D. None of these

Answer 1

Answer: (D)

Since, $2{\cos }^{-1}x={\cos }^{-1}(2x^2-1)$ Therefore, $2{\cos }^{-1}0.8={\cos }^{-1}(2\times 0.64-1)={\cos }^{-1}(0.28)$ $\Rightarrow$ $\cos (2{\cos }^{-1}0.8)=\cos ({\cos }^{-1}0.28)=0.28$