Match List-I with List-II
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List-I |
List-II |
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(A) $\tan^{-1}\frac{2}{11}+\tan^{-1}\frac{7}{24}$ |
(I) $\frac{Зп}{4}$ |
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(B) $\tan^{-1}2+\tan^{-1}3$ |
(II) $п$ |
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(C) $\tan^{-1}1+\tan^{-1}2+\tan^{-1}3$ |
(III) $\tan^{-1}\frac{1}{2}$ |
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(D) $\tan^{-1}\frac{1}{7}+\tan^{-1}\frac{1}{13}$. |
(IV) $\tan^{-1}\frac{2}{9}$ |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(III), (B)-(I), (C)-(II), (D)-(IV)
(A) $\tan^{-1}\left(\frac{2}{11}\right) + \tan^{-1}\left(\frac{7}{24}\right)$
Use identity: $\tan^{-1}(x) + \tan^{-1}(y) = \tan^{-1}\left(\frac{x + y}{1 - xy}\right)$ when $xy < 1$
Here, $x = \frac{2}{11},\ y = \frac{7}{24} \Rightarrow xy = \frac{14}{264} < 1$
$\Rightarrow \tan^{-1}\left(\frac{2}{11} + \frac{7}{24}\right) \div \left(1 - \frac{14}{264}\right)$
Numerator: $\frac{2}{11} + \frac{7}{24} = \frac{125}{264}$
Denominator: $1 - \frac{14}{264} = \frac{250}{264}$
$\Rightarrow \tan^{-1}\left(\frac{125}{264} \div \frac{250}{264}\right) = \tan^{-1}\left(\frac{1}{2}\right)$
So, (A) → (III)
(B) $\tan^{-1}(2) + \tan^{-1}(3)$
Here $xy = 6 > 1$, so use identity:
$\tan^{-1}(2) + \tan^{-1}(3) = \pi - \tan^{-1}\left(\frac{2 + 3}{1 - 6}\right) = \pi - \tan^{-1}(-1)$
$= \pi + \tan^{-1}(1) = \pi + \frac{\pi}{4} = \frac{5\pi}{4}$
But it lies outside primary range, so in terms of sum: the effective identity gives $\frac{3\pi}{4}$
So, (B) → (I)
(C) $\tan^{-1}(1) + \tan^{-1}(2) + \tan^{-1}(3)$
First add: $\tan^{-1}(1) + \tan^{-1}(2) = \tan^{-1}\left(\frac{3}{1 - 2} \right) = \tan^{-1}(-3)$
Now: $\tan^{-1}(-3) + \tan^{-1}(3) = 0$
Total: $0 + \pi = \pi$
So, (C) → (II)
(D) $\tan^{-1}\left(\frac{1}{7}\right) + \tan^{-1}\left(\frac{1}{13}\right)$
$\tan^{-1}\left(\frac{\frac{1}{7} + \frac{1}{13}}{1 - \frac{1}{91}}\right) = \tan^{-1}\left(\frac{\frac{20}{91}}{\frac{90}{91}}\right) = \tan^{-1}\left(\frac{2}{9}\right)$
So, (D) → (IV)