How to differentiate y=sec 2x ?

##dy/dx=2sec2xtan2x##
Ideas to use:
-> ##dy/dx=dy/(du)*(du)/dx## (this is the chain rule)
-> ##d/dx(secx)=secxtanx## (Click here for an explanation of this result https://socratic.org/calculus/differentiating-trigonometric-functions/derivatives-of-y-sec-x-y-cot-x-y-csc-x)
->There will also be a substitution
How to do it:
##y=secu## where ##u=2x##
##dy/(du)=secutanu## and ##(du)/dx=2##
Recall ##dy/dx=dy/(du)*(du)/dx##
Therefore ##dy/dx=secutanu*2=2sec2xtan2x##