What is a common mistake when solving a quadratic equation using the quadratic formula?

Adding the entire b² - 4ac term to the numerator instead of putting it under a square root.

Forgetting to divide the entire numerator by 2a, often only dividing the square root portion instead.

Multiplying the entire b² - 4ac term by an extra factor of 4 before placing it under the square root.

Squaring the entire quadratic formula expression on both sides to eliminate the fraction.