Вариант 15 ИДЗ 5.2

EDS - 5.2
№1.15. Prove that the functions f (x) = cos7x - cosx; φ (x) = 2x2 as x → 0 are infinitesimal of the same order of smallness.
№2.15 Find the limits.
№3.15 Investigate these functions for continuity and build their graphs.
№4.15 Investigate these functions for continuity at the specified points. f (x) = ....; x1 = 0; x2 = 1.