Angles of a triangle

Did you know ? Nikolay Ivanovich Lobachevsky was a Russian mathematician, co-creator of non-Euclidean geometry: Lobachevsky's geometry has the same axioms as Euclidean geometry, except for the axiom about parallel lines. In Lobachevski's geometry, it is postulated that through a point that does not lie on the line a, it is possible to draw at least two straight lines that do not intersect the line a in the given plane determined by this point and the line (it follows from this that there are infinitely many of them).