Question

What are common mistakes students make when using the quadratic formula?

Answer 1

Here are a couple of them.

Explanation:

Mistakes in memorization

The denominator `2a` is under the sum/difference. It is not just under the square root.

Ignoring signs

If `a` is positive but `c` is negative, then `b^2-4ac` will be the sum of two positive numbers. (Assuming that you have real number coefficients.)