JEE MAIN - Mathematics (2023 - 30th January Morning Shift - No. 7)
If the solution of the equation $$\log _{\cos x} \cot x+4 \log _{\sin x} \tan x=1, x \in\left(0, \frac{\pi}{2}\right)$$, is $$\sin ^{-1}\left(\frac{\alpha+\sqrt{\beta}}{2}\right)$$, where $$\alpha$$, $$\beta$$ are integers, then $$\alpha+\beta$$ is equal to :
3
6
4
5
Explanation
$${\log _{\cos x}}\cot x + 4{\log _{\sin x}}\tan x = 1$$
$$ \Rightarrow {\log _{\cos x}}\cot x - 4{\log _{\sin x}}\cot x = 1$$
$$ \Rightarrow 1 - {\log _{\cos x}}\sin x - 4 - 4{\log _{\sin x}}\cos x = 1$$
Let $${\log _{\cos x}}\sin x = t$$
$$t + {4 \over t} = 4$$
$$ \Rightarrow t = 2$$
$$\sin x = {\cos ^2}x$$
$$ \Rightarrow \sin x = 1 - {\sin ^2}x$$
$$ \Rightarrow {\sin ^2}x + \sin {x^{ - 1}} = 0$$
$$ \Rightarrow \sin x = {{ - 1\, \pm \,\sqrt 5 } \over 2}$$
as $$x \in \left( {0,{\pi \over 2}} \right)$$
$$\sin x = {{\sqrt 5 - 1} \over 2}$$
$$x = {\sin ^{ - 1}}\left( {{{ - 1 + \sqrt 5 } \over 2}} \right)$$
$$ \Rightarrow \alpha = - 1,\beta = 5$$
$$\alpha + \beta = 4$$
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