gauthmath.

 I was preparing for a geometry exam and felt that my knowledge was insufficient. I found a portal  gauthmath.net with step-by-step solutions and decided to give it a try. What I liked most was that they explained not only “how” but also “why” the problem was solved that way. In algebra, I figured out systems of equations, and in calculus, I figured out limits. Now, when I encounter similar examples, I can solve them myself. It's a very useful resource, especially for self-study.