Example 2. Answer the following questions:
(1) $\sqrt{6^{2}}=6$, is this correct?
(2) $\sqrt{(-6)^{2}}=-6$, is this correct?
Answer: (1) Yes, (2) No.
Example 2 can be easily generalized to the general case: the square root of a number $a$ squared is the absolute value of the number $a$, that is,
$$
\sqrt{a^{2}}=|a|=\left(\begin{array}{ll}
a ; & (a>0) \\
0, & (a=0) \\
-a, & (a<0)
\end{array}\right.
$$

With this general conclusion, the solution to the following type of problem becomes straightforward.