To evaluate the integral \(\int \frac{\cos (5 x)}{4 \sin (5 x)+7} \, dx\), we can use a substitution method. Let \(u = 4 \sin(5x) + 7\). Then, find \(du\) and rewrite the integral in terms of \(u\).
Step 1: Substitution
Let \( u = 4 \sin(5x) + 7 \). Then, we need to find \( du \).
Step 2: Differentiate \( u \)
Differentiate \( u \) with respect to \( x \):
\[
\frac{du}{dx} = 4 \cdot 5 \cos(5x) = 20 \cos(5x)
\]
Thus,
\[
du = 20 \cos(5x) \, dx
\]
Step 3: Rewrite the Integral
Rewrite the integral in terms of \( u \):
\[
\int \frac{\cos(5x)}{4 \sin(5x) + 7} \, dx = \int \frac{1}{20} \cdot \frac{1}{u} \, du
\]
Step 4: Integrate
Integrate with respect to \( u \):
\[
\int \frac{1}{20} \cdot \frac{1}{u} \, du = \frac{1}{20} \int \frac{1}{u} \, du = \frac{1}{20} \ln|u| + C
\]
Step 5: Substitute Back
Substitute \( u = 4 \sin(5x) + 7 \) back into the integral:
\[
\frac{1}{20} \ln|4 \sin(5x) + 7| + C
\]