Relativistic mass and E=mc2

Okay so for the past two days i have looked up how to derive e=mc2 by curiosity. To make things clear I am 17 and i am in year 12 doing further maths chemistry and physics, so i dont have much knowledge about relativity overall, I have only looked up the derivation of E=mc2. I get most of the things and i went back to the lorentz transform, to be exact i learnt how to derive the lorentz factor. But my problem is that i dont understand how the relativistic mass equals to initial mass times by the lorentz factor (gamma) and i looked online but i couldnt find a clear explaination about why it is, because when i looked at how to derive e=mc2 it uses the relativistic mass equation and i dont really understand where that comes from. I have only found that m(rel)=m initial x lorentz factor but i dont know why it is so could someone (if possible) provide a simple explaination or if possible a not too complicated derivation of the relativistic mass equation so that i could possibly understand why it is, because i dont know much about relativity, i just picked out one thing of it to kind of learn it because it seems interesting but this is the only thing that i was struggling to understand. I am posting this on the Uni courses forum because i dont think anyone would know this in the A-level section or im not sure but im quite new to the student room. Thanks

Idk if this would interest you, but I recommend reading "Why does e=mc2" by Brian Cox. Already halfway through it and it's pretty good so far, it's all explained gradually and in a fairly simple way. I'm also in year 12 and take the exact same subjects :biggrin: