Choose the CORRECT set of functions, which are linearly

1. sin x, sin² x and cos² x
2. cos x, sin x and tan x
3. cos 2x, sin² x and cos² x
4. cos 2x, sin x and cos x

Going by options,
cos 2x = 2cos² x – 1 =2 cos² x – (sin² x + cos² x)
cos 2x = cos²x – sin² x