Question 63297
Given 2x^2 - 18 = 0

Add 18 on both sides, we get

2x^2 -18 +18  = 0 +18

2x^2 = 18

Divide by 2, we get

2x^2 / 2 = 18 /2

x^2 = 9

Take the square root,

we get sqrt(x^2) =  sqrt(9)

x = + 3 or  -3

Whenever we take the square root, we get two values one with positive sign and one with negative sign.