§ 27: 27.4

27.4 Розв’яжіть рівняння:

1) cos2x = –12; 2x = ± arccos12 + 2πn, n ∈ Z; 2x = ± π3 + 2πn, n ∈ Z;

x =± π3 + 2πn, n ∈ Z;

2) cosx5 = –32; x5 = ± arccos(–32) + 2πn, n ∈ Z;

x5 = ± (π – arccos32) + 2πn, n ∈ Z; x5 = ±(π – π6) + 2πn, n ∈ Z;

x5 = ± 5π6 + 2πn, n ∈ Z; x = ± 25π6 + 10πn, n ∈ Z;

3) cos3x4 = –1; 3x4 = π + 2πn, n ∈ Z; x = 4π3 + 8πn3, n ∈ Z.