I'm getting into differential equations and I am currently watching this video while trying to solve some problems: https://www.khanacademy.org/math/dif...tial-equations

He ends up with

$\displaystyle (1-y^2)dy=x^2\cdot dx$

and says: "now we can integrate".

Why can't I simply integrate dy/dx? I'm not completely oblivious as to what is going on, but I'm just trying to get the details right.

Thanks!