integral of sec(x), 4 results,
tanh^-1(sin(x))=ln|sec(x)+tan(x)|, https://www.youtube.com/watch?v=Tpl6pCwDwKI ,
complex defintion of sine & cosine, https://www.youtube.com/watch?v=CjQTWtW_x9o ,
4 ways to integrate sec(x),
integral of 1/cos(x),
integral of sec(x) without that trick,
blackpenredpen,
math for fun,