Subtract 30, then factor the equation.
... x² = 30
... x² - 30 = 0
... (x -√30)(x +√30) = 0
By the zero product rule, the solutions are values of x that make a factor be zero.
... x - √30 = 0 . . . . the first factor is zero
... x = √30
... x + √30 = 0 . . . . the second factor is zero
... x = -√30
The solutions are . . .
... x = ±√30 . . . . . matches your 3rd choice