Hi Sergei! What a great start :) Loving math, I think it would also be fun to alert Alex to obtuse angles, larger than 90 degrees. In fact, what he is not highlighting is also an angle :) If you cut a piece out of a circular pie, both your piece, AND what is left represents angles. One is 360 degrees minus the degrees of the other. I will make a video and post in for you in @mattesommar!