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Let f(x)=max{tanx, cotx}. Then the numbe...

Let `f(x)=max{tanx, cotx}`. Then the number of roots of the equation `f(x)=(1)/(2)" in "(0, 2pi)` is

A

0

B

1

C

2

D

4

Text Solution

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The correct Answer is:
To solve the problem, we need to analyze the function \( f(x) = \max\{\tan x, \cot x\} \) and find the number of roots of the equation \( f(x) = \frac{1}{2} \) in the interval \( (0, 2\pi) \). ### Step-by-Step Solution: 1. **Understand the Functions**: - The function \( f(x) \) is defined as the maximum of \( \tan x \) and \( \cot x \). - We need to analyze both \( \tan x \) and \( \cot x \) over the interval \( (0, 2\pi) \). 2. **Identify Key Points**: - The functions \( \tan x \) and \( \cot x \) have vertical asymptotes at \( x = \frac{\pi}{2} \) and \( x = \frac{3\pi}{2} \) respectively. - The points where \( \tan x = \cot x \) can be found by solving \( \tan x = \cot x \), which simplifies to \( \tan^2 x = 1 \). This gives us \( x = \frac{\pi}{4} \) and \( x = \frac{5\pi}{4} \). 3. **Graph the Functions**: - Sketch the graphs of \( \tan x \) and \( \cot x \) in the interval \( (0, 2\pi) \): - From \( 0 \) to \( \frac{\pi}{2} \), \( \tan x \) increases from \( 0 \) to \( +\infty \) and \( \cot x \) decreases from \( +\infty \) to \( 0 \). - From \( \frac{\pi}{2} \) to \( \frac{3\pi}{2} \), \( \tan x \) decreases from \( -\infty \) to \( 0 \) and \( \cot x \) increases from \( 0 \) to \( +\infty \). - From \( \frac{3\pi}{2} \) to \( 2\pi \), \( \tan x \) increases from \( 0 \) to \( +\infty \) and \( \cot x \) decreases from \( +\infty \) to \( 0 \). 4. **Determine the Maximum Function**: - In the interval \( (0, \frac{\pi}{2}) \), \( f(x) = \tan x \). - In the interval \( (\frac{\pi}{2}, \frac{3\pi}{2}) \), \( f(x) = \cot x \). - In the interval \( (\frac{3\pi}{2}, 2\pi) \), \( f(x) = \tan x \). 5. **Find the Intersection with \( y = \frac{1}{2} \)**: - In \( (0, \frac{\pi}{2}) \), we set \( \tan x = \frac{1}{2} \). This will have one solution since \( \tan x \) is continuous and increasing. - In \( (\frac{\pi}{2}, \frac{3\pi}{2}) \), we set \( \cot x = \frac{1}{2} \). This will also have one solution since \( \cot x \) is continuous and decreasing. - In \( (\frac{3\pi}{2}, 2\pi) \), we set \( \tan x = \frac{1}{2} \). This will have one solution as well. 6. **Count the Total Roots**: - From the analysis, we find: - One root in \( (0, \frac{\pi}{2}) \) - One root in \( (\frac{\pi}{2}, \frac{3\pi}{2}) \) - One root in \( (\frac{3\pi}{2}, 2\pi) \) - Thus, the total number of roots of the equation \( f(x) = \frac{1}{2} \) in the interval \( (0, 2\pi) \) is **3**. ### Conclusion: The number of roots of the equation \( f(x) = \frac{1}{2} \) in the interval \( (0, 2\pi) \) is **3**.
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