Question

The general solution of the equation $2 \cos 2 x=3.2 \cos ^2 x-4$ is

• A. $x=2 n \pi, n \in I$
• B. $x=n \pi, n \in I$
• C. $x=\frac{n \pi}{4}, n \in I$
• D. $x=\frac{n \pi}{2}, n \in I$

Answer 1

Answer: (B)

$2 \cos 2 x=6 \cos ^2 x-4$
$\Rightarrow 2\left(2 \cos ^2 x-1\right)=6 \cos ^2 x-4$
$\Rightarrow 2 \cos ^2 x=2 \Rightarrow \cos ^2 x=1 \Rightarrow x=n \pi$