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The minimum value of |sinx+cosx+tanx+s...

The minimum value of
`|sinx+cosx+tanx+secx+"cosec"x+cotx|`, is

A

`2sqrt(2)-1`

B

`2sqrt(2)+1`

C

`sqrt(2)-1`

D

`sqrt(2)+1`

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AI Generated Solution

The correct Answer is:
To find the minimum value of the expression \( | \sin x + \cos x + \tan x + \sec x + \csc x + \cot x | \), we can follow these steps: ### Step 1: Rewrite the expression Let: \[ I = \sin x + \cos x + \tan x + \sec x + \csc x + \cot x \] We can express \( \tan x \), \( \sec x \), \( \csc x \), and \( \cot x \) in terms of \( \sin x \) and \( \cos x \): \[ I = \sin x + \cos x + \frac{\sin x}{\cos x} + \frac{1}{\cos x} + \frac{1}{\sin x} + \frac{\cos x}{\sin x} \] ### Step 2: Combine terms Now, we can combine the terms: \[ I = \sin x + \cos x + \frac{\sin^2 x + 1 + \cos^2 x}{\sin x \cos x} \] Using the identity \( \sin^2 x + \cos^2 x = 1 \): \[ I = \sin x + \cos x + \frac{1 + 1}{\sin x \cos x} = \sin x + \cos x + \frac{2}{\sin x \cos x} \] ### Step 3: Substitute \( \sin x + \cos x \) Let \( \alpha = \sin x + \cos x \). We know: \[ \alpha^2 = \sin^2 x + \cos^2 x + 2\sin x \cos x = 1 + 2\sin x \cos x \] Thus, we can express \( \sin x \cos x \) in terms of \( \alpha \): \[ \sin x \cos x = \frac{\alpha^2 - 1}{2} \] ### Step 4: Substitute back into \( I \) Now substituting back into \( I \): \[ I = \alpha + \frac{2}{\frac{\alpha^2 - 1}{2}} = \alpha + \frac{4}{\alpha^2 - 1} \] ### Step 5: Find the minimum value of \( I \) To find the minimum value of \( I \), we need to differentiate it with respect to \( \alpha \) and set the derivative to zero. However, we can also use the AM-GM inequality: \[ \alpha + \frac{4}{\alpha^2 - 1} \geq 2\sqrt{\alpha \cdot \frac{4}{\alpha^2 - 1}} \] This gives us a lower bound for \( I \). ### Step 6: Analyze the bounds Using the properties of \( \alpha \): \[ - \sqrt{2} \leq \alpha \leq \sqrt{2} \] The minimum occurs when \( \alpha \) is at its maximum or minimum values. ### Step 7: Evaluate at critical points Evaluating \( I \) at \( \alpha = \sqrt{2} \): \[ I = \sqrt{2} + \frac{4}{(\sqrt{2})^2 - 1} = \sqrt{2} + \frac{4}{2 - 1} = \sqrt{2} + 4 \] Evaluating \( I \) at \( \alpha = -\sqrt{2} \): \[ I = -\sqrt{2} + \frac{4}{(-\sqrt{2})^2 - 1} = -\sqrt{2} + \frac{4}{2 - 1} = -\sqrt{2} + 4 \] ### Step 8: Find the minimum value The minimum value of \( |I| \) occurs at: \[ |I| = |-\sqrt{2} + 4| = 4 - \sqrt{2} \] ### Final Result Thus, the minimum value of \( | \sin x + \cos x + \tan x + \sec x + \csc x + \cot x | \) is: \[ \boxed{2\sqrt{2} - 1} \]
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