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Match List-I with List-II

List-IList-II
Inverse Trigonometric functionPrincipal values of arguments
(A) sin−1(−12)sin^{-1}\left(\frac{-1}{2}\right)(I) −π3\frac{-\pi}{3}
(B) cos−1(−12)cos^{-1}\left(\frac{-1}{2}\right)(II) 3π4\frac{3\pi}{4}
(C) tan−1(−3)tan^{-1}(-\sqrt{3})(III) −π6\frac{-\pi}{6}
(D) sec−1(−2)sec^{-1}(-\sqrt{2})(IV) 2π3\frac{2\pi}{3}

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

The principal value ranges for inverse trigonometric functions are:

sin⁡−1(x)\sin^{-1}(x): [−π2,π2][-\frac{\pi}{2}, \frac{\pi}{2}]

cos⁡−1(x)\cos^{-1}(x): [0,π][0, \pi]

tan⁡−1(x)\tan^{-1}(x): (−π2,π2)(-\frac{\pi}{2}, \frac{\pi}{2})

sec⁡−1(x)\sec^{-1}(x): [0,π]−{π2}[0, \pi] - \{\frac{\pi}{2}\}


For sin⁡−1(−12)\sin^{-1}(\frac{-1}{2}):

Since sin⁡(π6)=12\sin(\frac{\pi}{6}) = \frac{1}{2}, and sine is negative:

sin⁡(−π6)=−12\sin(-\frac{\pi}{6}) = -\frac{1}{2}

The value −π6-\frac{\pi}{6} lies in the range [−π2,π2][-\frac{\pi}{2}, \frac{\pi}{2}].

Therefore, sin⁡−1(−12)=−π6\sin^{-1}(\frac{-1}{2}) = -\frac{\pi}{6}

(A) matches with (III)


For cos⁡−1(−12)\cos^{-1}(\frac{-1}{2}):

Since cos⁡(π3)=12\cos(\frac{\pi}{3}) = \frac{1}{2}, and cosine is negative:

In the second quadrant, cos⁡(2π3)=−12\cos(\frac{2\pi}{3}) = -\frac{1}{2}

The value 2π3\frac{2\pi}{3} lies in the range [0,π][0, \pi].

Therefore, cos⁡−1(−12)=2π3\cos^{-1}(\frac{-1}{2}) = \frac{2\pi}{3}

(B) matches with (IV)


For tan⁡−1(−3)\tan^{-1}(-\sqrt{3}):

Since tan⁡(π3)=3\tan(\frac{\pi}{3}) = \sqrt{3}, and tangent is negative:

tan⁡(−π3)=−3\tan(-\frac{\pi}{3}) = -\sqrt{3}

The value −π3-\frac{\pi}{3} lies in the range (−π2,π2)(-\frac{\pi}{2}, \frac{\pi}{2}).

Therefore, tan⁡−1(−3)=−π3\tan^{-1}(-\sqrt{3}) = -\frac{\pi}{3}

(C) matches with (I)


For sec⁡−1(−2)\sec^{-1}(-\sqrt{2}):

Since sec⁡(θ)=1cos⁡(θ)\sec(\theta) = \frac{1}{\cos(\theta)}:

cos⁡(θ)=−12=−22\cos(\theta) = \frac{-1}{\sqrt{2}} = \frac{-\sqrt{2}}{2}

Since cos⁡(π4)=22\cos(\frac{\pi}{4}) = \frac{\sqrt{2}}{2}:

In the second quadrant, cos⁡(3π4)=−22\cos(\frac{3\pi}{4}) = -\frac{\sqrt{2}}{2}

The value 3π4\frac{3\pi}{4} lies in the range [0,π]−{π2}[0, \pi] - \{\frac{\pi}{2}\}.

Therefore, sec⁡−1(−2)=3π4\sec^{-1}(-\sqrt{2}) = \frac{3\pi}{4}

(D) matches with (II)


Final matching:

(A) → (III)

(B) → (IV)

(C) → (I)

(D) → (II)

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