Using the quadratic formula can be tricky, and many students make the same mistakes. Here are some common ones to watch out for:

1. Mixing Up Numbers: When you use the formula, make sure you know which numbers are $a$, $b$, and $c$ in the equation $ax^2 + bx + c = 0$. If you mix them up, you might get the wrong answer!

2. Mistakes with the Discriminant: Don’t forget to calculate $b^2 - 4ac$ correctly. If you make a mistake with the signs here, it can mess up your whole solution.

3. Not Simplifying Your Answer: After you find the square root, make sure you simplify it. This step is important for getting the final answer right.

4. Overlooking Complex Solutions: If you find that $b^2 - 4ac$ is less than zero, this means you'll have complex roots. It's really important to recognize this!

Always remember to check your work to make sure everything is correct!