Step 1: Recognizing the Integral Form
The given integral is:
\[
\int \sqrt{x^2 + a^2} \, dx
\]
This is a standard integral, and the solution can be derived using the substitution method.
Step 2: Apply Integration Formula
The integral \( \int \sqrt{x^2 + a^2} \, dx \) has a standard solution:
\[
\int \sqrt{x^2 + a^2} \, dx = \frac{x \sqrt{x^2 + a^2}}{2} + \frac{a^2 \log |x + \sqrt{x^2 + a^2}|}{2}
\]
Step 3: Conclusion
Thus, the solution to the integral is \( \frac{x \sqrt{x^2 + a^2}}{2} + \frac{a^2 \log |x + \sqrt{x^2 + a^2}|}{2} \).