

Is this even a correct mindset to study math?
How you people study math?
I'm a self study person and would like to hear some suggestions from people who are doing math professionally.
This is how I study.
I usually study the theory part first and try to understand the core concepts and stuff like that and go for the examples and try them all of my own. Most of the time I come to the answer atleast have a idea how to initiate or set up.
But some time I'll have zero idea even after seeing the result that why they start that answer like that to prove something (it is this fact that I'm not able to start a proof by myself is exactly what bothers me each time) It seems they picked it out of blue and never in a million year I'll start with this argument because I don't see why they start with that idea at first place(I attached example below).Then I start to question that is my theory part even good? Do i really understood it? etc. All these just because I don't exactly see/know how to start a proof.
For eg take the one I showed in the pic. I will never start the procedure of taking BC× on both sides even if I give my self a whole day to prove that result.
Is this how people usually study or I'm Missing some core understanding or something?
It really frustrates me.
TIA :)