When using the Pythagorean theorem with right triangles, students often make some common mistakes. Here are a few to keep in mind:

1. Mixing Up the Sides: Remember, the theorem is only for right triangles. Make sure to find the right angle and label the sides correctly—$a$ and $b$ are the legs, and $c$ is the hypotenuse (the longest side).

2. Using the Wrong Formula: The correct formula is $a^2 + b^2 = c^2$. Always check that you’re putting the right numbers in. Some students accidentally add or subtract instead of squaring the sides.

3. Forgetting About Units: Always use units when measuring. If one side is in feet and another is in meters, you can't just put those numbers into the formula. Make sure to change all measurements to the same unit first.

4. Making Calculation Mistakes: Everyone makes simple math errors. It’s really important to double-check your work, especially when squaring numbers or finding square roots to get lengths.

5. Misunderstanding the Results: Sometimes, students forget to think about what their final answer means in the context of the problem. Make sure to understand your answer based on the situation you’re working on.

By keeping these mistakes in mind, you can use the Pythagorean theorem more effectively in your geometry problems!