Gujarat BoardEnglish MediumSTD 12 ScienceMathsInverse Trigonometric Functions1 Mark
MCQ
Find the principal value of: $\tan ^{-1}(-1)$.
✓
$-\frac{\pi}{4}$
B
$\frac{\pi}{4}$
C
$\frac{\pi}{3}$
D
$\frac{\pi}{6}$
✓
Answer
Correct option: A.
$-\frac{\pi}{4}$
(a): Let $\tan ^{-1}(-1)=x \Rightarrow-1=\tan x$ We know that the range of principal value branch of $\tan ^{-1}$ is $\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)$. Then, $-1=\tan \left(-\frac{\pi}{4}\right)$, where $-\frac{\pi}{4} \in\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)$ Hence, the principal value of $\tan ^{-1}(-1)$ is $-\frac{\pi}{4}$.
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