I would use the square root method because there is a power of 2 and constants without a variable power of 1.
The "best" method to solve a quadratic equation when there are only x² terms is the square root method. That suggests that nowhere in the equation there is any x term being raised to the first power.
The constants are kept on the other side of the equation while the x2 terms are generally collected on one side of the equation.
Taking the square roots of both sides to solve for the value of x is the logical next step after completing the previous step. When you find the square root of a constant, you must always add the "±" symbol.
2x² - 7 = 9
2x² = 9 + 7
2x² = 16
x² = 16/2
x² = 8
x = √8
x = 2√2
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