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JEE Main
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Mathematics
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Basics of Mathematics

JEE Main · Mathematics · Basics of Mathematics

If the solution of the equation _ x ( x) + 4 _ x ( x) = 1, x ∈ (0,...

If the solution of the equation log⁡tan⁡x(sin⁡x)+4log⁡sec⁡x(csc⁡x)=1,x∈(0,π2)∖{π4}\log_{\tan x}(\sin x) + 4 \log_{\sec x}(\csc x) = 1, x \in \left(0, \dfrac{\pi}{2}\right) \setminus \left\{\dfrac{\pi}{4}\right\} is x=sec⁡−1(α+β2)x = \sec^{-1}\left(\dfrac{\alpha + \sqrt{\beta}}{2}\right), where α,β\alpha, \beta are integers, then α+β\alpha + \beta is equal to:

Options

  1. A44
  2. B66
  3. C55
  4. D77

Correct answer

B. 66

Step-by-step solution

Given equation: log⁡tan⁡x(sin⁡x)+4log⁡sec⁡x(csc⁡x)=1\log_{\tan x}(\sin x) + 4 \log_{\sec x}(\csc x) = 1

We know that sin⁡x=tan⁡xsec⁡xand\sin x = \dfrac{\tan x}{\sec x} and\csc x = \dfrac{\sec x}{\tan x}.<br><br>Substitutingtheseintotheequation:<br><br>.<br><br>Substituting these into the equation:<br><br>\log_{\tan x}\left(\dfrac{\tan x}{\sec x}\right) + 4 \log_{\sec x}\left(\dfrac{\sec x}{\tan x}\right) = 1<br><br>Usingthequotientruleforlogarithms:<br><br>(1−log⁡tan⁡x(sec⁡x))+4(1−log⁡sec⁡x(tan⁡x))=1<br><br>Using the quotient rule for logarithms:<br><br>\left(1 - \log_{\tan x}(\sec x)\right) + 4 \left(1 - \log_{\sec x}(\tan x)\right) = 1

Let t=log⁡tan⁡x(sec⁡x)t = \log_{\tan x}(\sec x). Then log⁡sec⁡x(tan⁡x)=1t\log_{\sec x}(\tan x) = \dfrac{1}{t}.

The equation becomes:

1−t+4−4t=11 - t + 4 - \dfrac{4}{t} = 1

4−t−4t=04 - t - \dfrac{4}{t} = 0

t2−4t+4=0t^2 - 4t + 4 = 0

(t−2)2=0  ⟹  t=2(t - 2)^2 = 0 \implies t = 2

So, log⁡tan⁡x(sec⁡x)=2  ⟹  sec⁡x=tan⁡2x\log_{\tan x}(\sec x) = 2 \implies \sec x = \tan^2 x

Using the identity tan⁡2x=sec⁡2x−1\tan^2 x = \sec^2 x - 1:

sec⁡x=sec⁡2x−1  ⟹  sec⁡2x−sec⁡x−1=0\sec x = \sec^2 x - 1 \implies \sec^2 x - \sec x - 1 = 0

Solving this quadratic equation for sec⁡x\sec x:

sec⁡x=1±1−4(1)(−1)2=1±52\sec x = \dfrac{1 \pm \sqrt{1 - 4(1)(-1)}}{2} = \dfrac{1 \pm \sqrt{5}}{2}

Since x∈(0,π2)∖{π4}x \in \left(0, \dfrac{\pi}{2}\right) \setminus \left\{\dfrac{\pi}{4}\right\}, we have sec⁡x>1\sec x > 1.

Thus, we reject the negative root, giving sec⁡x=1+52\sec x = \dfrac{1 + \sqrt{5}}{2}.

This means x=sec⁡−1(1+52)x = \sec^{-1}\left(\dfrac{1 + \sqrt{5}}{2}\right).

Comparing with x=sec⁡−1(α+β2)x = \sec^{-1}\left(\dfrac{\alpha + \sqrt{\beta}}{2}\right), we get α=1\alpha = 1 and β=5\beta = 5.

Therefore, α+β=1+5=6\alpha + \beta = 1 + 5 = 6.

Answer: 66
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