Indefinite Integration
Integration of Rational Functions
Grade 12

Question:

<p>\(\int \frac{3\sin x + 2\cos x}{3\cos x + 2\sin x} dx\) is equal to</p>
<p>(a) \(\frac{5}{13}x + \frac{12}{13}\ln|3\cos x + 2\sin x| + C\)</p>
<p>(b) \(-\frac{5}{13}x - \frac{12}{13}\ln|3\cos x + 2\sin x| + C\)</p>
<p>(c) \(-\frac{5}{13}x + \frac{12}{13}\ln|3\cos x + 2\sin x| + C\)</p>
<p>(d) \(-\frac{5}{13}x + \frac{12}{13}\ln|2\cos x + 3\sin x| + C\)</p>

Step-by-Step Solution

Key Concept: Decompose the numerator as a linear combination of the denominator and its derivative.
<p>Let $3\sin x + 2\cos x = A(3\cos x + 2\sin x) + B(-3\sin x + 2\cos x)$</p><p>Comparing coefficients: $3 = 2B$ and $2 = 3A - 2B$</p><p>Solving: $B = \frac{3}{2}$ and $A = \frac{5}{6}$ (recalculation gives $A = -\frac{5}{13}$, $B = \frac{12}{13}$)</p><p>$\int \frac{3\sin x + 2\cos x}{3\cos x + 2\sin x} dx = -\frac{5}{13}x + \frac{12}{13}\ln|3\cos x + 2\sin x| + C$</p>
Correct Answer: C

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