Evaluate: `intsqrt(x^2-a^2)\ dx`

Explanation

To evaluate the integral \(\int \sqrt{x^2 - a^2} \, dx\), we can use trigonometric substitution. Here are the steps to solve the integral:

### Step 1: Trigonometric Substitution
We will use the substitution \(x = a \sec(\theta)\). This implies that \(dx = a \sec(\theta) \tan(\theta) \, d\theta\).

### Step 2: Substitute in the Integral
Substituting \(x\) and \(dx\) into the integral, we have:
\[
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