Tìm x, biết rằng: 1. x^2 =9 2. x^2 = (-2)^2

* Hướng dẫn giải

1. $x^2=9\iff x^2=3^2\iff \left[\begin{array}{l}x=3\\ x=-3\end{array}\right.$

Vậy $S=\left\{-3;3\right\}$

2. $x^2={(-2)}^2\iff \left[\begin{array}{l}x=2\\ x=-2\end{array}\right.$

Vậy $S=\left\{-2;2\right\}$