Getting hung up on some trig-solving...

For the first problem here, we get 8x-2sec^2(x) when derived and then you set that equal to 0 to find the critical points. I have no clue at all how to solve that.

The second, you get -8sin(x)+4cos^2(x) when taking the derivative. Again, set it equal to 0 and then I'm stumped.

Feels bad that this is just algebra, but I dunno what to do. Will greatly appreciate any help!