Question:
Evaluate the following integrals:
$\int \frac{\cos x}{2+3 \sin x} d x$
Solution:
Assume $2+3 \sin x=t$
$d(2+3 \sin x)=d t$
$3 \cos x d x=d t$
$\cos x d x=\frac{d t}{3}$
Put $t$ and dt in given equation we get
$\Rightarrow \frac{1}{3} \int \frac{\mathrm{dt}}{\mathrm{t}}$
$=\frac{1}{3} \ln |\mathrm{t}|+\mathrm{c}$
But $t=2+3 \sin x$
$=\frac{1}{3} \ln |2+3 \sin x|+c$