Definite Integration
Finding Parameters
Grade 12

Question:

<p>If <span class="math">\int_0^{\pi/3} \frac{\tan\theta}{2k\sec\theta} d\theta = 1 - \frac{1}{\sqrt{2}}</span>, (<span class="math">k > 0</span>), then the value of <span class="math">k</span> is</p>
<p>(a) <span class="math">1</span></p>
<p>(b) <span class="math">\frac{1}{2}</span></p>
<p>(c) <span class="math">2</span></p>
<p>(d) <span class="math">4</span></p>

Step-by-Step Solution

Key Concept: Simplify the trigonometric expression and integrate directly, then solve for the parameter.
<p>Simplify: <span class="math">\frac{\tan\theta}{2k\sec\theta} = \frac{\sin\theta}{2k\cos\theta} \cdot \cos\theta = \frac{\sin\theta}{2k}</span></p><p>So: <span class="math">\int_0^{\pi/3} \frac{\sin\theta}{2k} d\theta = \frac{1}{2k}[-\cos\theta]_0^{\pi/3} = \frac{1}{2k}\left(-\frac{1}{2} + 1\right) = \frac{1}{4k}</span></p><p>Setting equal: <span class="math">\frac{1}{4k} = 1 - \frac{1}{\sqrt{2}}</span>, solve for <span class="math">k</span>.</p>
Correct Answer: A

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