Principal value ranges for inverse trigonometric functions:
sin−1(x): [−2π,2π]
cos−1(x): [0,π]
tan−1(x): (−2π,2π)
cot−1(x): (0,π)
For sin−1(−21):
Need an angle in [−2π,2π] whose sine equals −21.
Since sin(6π)=21 and sine is negative for negative angles:
sin(−6π)=−21
Therefore, sin−1(−21)=−6π → (II)
For cos−1(−21):
Need an angle in [0,π] whose cosine equals −21.
Since cos(3π)=21 and cosine is negative in the second quadrant:
π−3π
=33π−π
=32π
Therefore, cos−1(−21)=32π → (III)
For tan−1(−3):
Need an angle in (−2π,2π) whose tangent equals −3.
Since tan(3π)=3:
tan(−3π)=−3
Therefore, tan−1(−3)=−3π → (IV)
For cot−1(3):
Need an angle in (0,π) whose cotangent equals 3.
cot(6π)
=sin(6π)cos(6π)
=2123
=3
Therefore, cot−1(3)=6π → (I)
Final matching:
| Function | Principal Value |
|---|
| (A) sin−1(−21) | (II) −6π |
| (B) cos−1(−21) | (III) 32π |
| (C) tan−1(−3) | (IV) −3π |
| (D) cot−1(3) | (I) 6π |
Correct answer: (A)-(II), (B)-(III), (C)-(IV), (D)-(I)