Помогите пожалуйста с алгеброй, срочно!!!!

Question

Помогите пожалуйста с алгеброй, срочно!!!!

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Answer 1

1) cosx ≤ -√2/2
3π/4 + 2πn ≤ x ≤ 5π/4 + 2πn, n ∈ Z

2) cosx = √2/2
x = ±π/4 + 2πn, n ∈ Z
0 ≤ ±π/4 + 2πn < 3π, n ∈ Z
0 < ±1 + 8n < 12, n ∈ Z
n = 0; 1.
x₁ = -π/4;
x₂ = π/4
x₃ = -π/4 + 2π = 7π/4
x₄ = π/4 + 2π = 9π/4

Answer 2

Cosx≤-√2/2
3π/4+2πk≤x≤5π/4+2πk,k∈z

cosx=√2/2
x=-π/4+2πk U x=π/4+2πk
0≤-π/4+2πk≤3π
0≤-1+8k≤12
1≤8k≤13
1/8≤k≤13/8
k=1⇒x=-π/4+2π=7π/4
0≤π/4+2πk≤3π
0≤1+8k≤12
-1≤8k≤11
-1/8≤k≤11/8
k=0⇒x=π/4
k=1⇒x=π/4+2π=9π/4