A student writes the formula `sqrt(a b)=sqrt(a)\ sqrt(b)dot` Then he substitutes `a=-1\ a n d\ b=-1\ a n d\ ` finds `1=-1` . Explain where is he wrong?

Explanation

To solve the problem, we need to analyze the student's mistake step by step.

### Step 1: Understanding the Formula
The student starts with the formula:
\[ \sqrt{ab} = \sqrt{a} \cdot \sqrt{b} \]
This formula is true only when both \(a\) and \(b\) are non-negative real numbers.
...