# Which of the following is incorrect?

Question:

Which of the following is incorrect?

(a) $\sin \theta=-\frac{1}{5}$

(b) $\cos \theta=1$

(c) $\sec \theta=\frac{1}{2}$

(d) $\tan \theta=20$

Solution:

If $\sec \theta=\frac{1}{2}$

$\Rightarrow \cos \theta=2$

i. e $\theta=\cos ^{-1}(2)$

i.e No solution

$\therefore \sec \theta=\frac{1}{2}$ is incorrect

Hence, the correct answer is option C.