ModusOperandi is a great app for everyone learning math, as it provides real feedback on your own solution path.
Compared to other apps it does not solve an exercise for you, but really verifies it

Pros
- easy to use: solve with pen and paper, take a picture, get the verification
- gives explanations, videos and hints when you did a mistake
- capability to send problems to a tutor to get help if needed
- working great on simplifications, equations, integrals, derivatives...

Cons
- some math cannot be analyzed yet, like limits

I can highly recommend the app as it really helps to understand when you have done a mistake.