If a different result appears from before, at least one of your efforts, the original or the check, will be in error. Computer programs can perform arithmetic and algebraic or symbolic operations. They can also draw graphs and solve some equations rapidly. These programs do not provide solutions to all possible problems. For the solutions they can provide, you have to understand the statement of the initial problem.
Understanding is an personal affair.
No computer and no other person can do this for you. But if you know what to expect from a calculation, calculators and computer programs can help you check your expectations and explore mathematical ideas. Here you can learn from your mistakes. In some cases, computer software can tutor you. They can tell what to expect in various circumstances.