inverses

Here is a good problem solvers https://ncalculators.com/number-conversion/pythagoras-theorem.htm for pyragoream therom, and https://www.symbolab.com/solver/vector-calculator that give you step ny stem of how your sum was calculated it does all sorts, the best way to use https://www.symbolab.com/solver/vector-calculator is to type your sum in and cover your answer or supposed to be with your hand look at how its done then practice it yourself, after watching this sites video, and I also learn about that sum from youtube helps, it has tones of stuff, hope this helps.

I see your new welcome to Khan Academy, it helped me a lot hope you have luck to.