1. ## u substitution

What would I let "u" be in this case and why??

Evaluate the indefinite integral.

I dont know the integral button forgive me -> !sec 2x tan 2x dx

2. You sub $u = \sec{2x}$ because differentiating it produces $du = 2\sec{2x}\tan{2x}~dx$ and consequently:

$\int \sec{2x}\tan{2x}~dx=\frac{1}{2}\int du = \ldots$