Ryabushko A.P. IDZ 5.2 option 5

DHS - 5.2
№1.5 Prove that the function f (x) = cos 3x - cos x; φ (x) = 7x2 as x → 0 are the infinitesimal of the same order of smallness.
№2.5 Find limits.
№3.5 investigate these functions continuity and build their schedules.
№4.5 investigate these functions continuity at these points. f (x) = ....; x1 = 2; x2 = 3;