Question

If $f(x)=\left|\begin{array}{ccc}\text{Cos}x& 1& 0\\ 0& 2\cos x& 3\\ 0& 1& 2\cos x\end{array}\right|$ then $\underset{x\to \pi }{\lim }f(x)=$

• A. $-1$
• B. $1$
• C. $0$
• D. $3$

Answer 1

Answer: (A)

$f(x)=4{\cos }^{3}x-3\cos x$ $=\cos 3x$
$\underset{x\to \pi }{\lim }\cos 3x=\cos 3\pi$
$=-1$