To solve this you must completely isolate x. This means that you have to get rid of the square from the x. To do this take the square root of both sides (square root is the opposite of squaring something and will cancel the square from the x)
√x² = √9
x = 3
and
x = -3
Check:
3² = 9
3*3 = 9
9 = 9
(-3)² = 9
-3 * -3 = 9
9 = 9
Hope this helped!
~Just a girl in love with Shawn Mendes