а) sinx ≥ -sqrt(2)/2 б) cos4x ≤ sqrt(3)/2
a) (-π/4)+2πn ≤ x ≤ (5π/4)+2πn, n ∈ Z см. рис. б) (π/6)+2πn ≤ [b]4[/b]x ≤ (11π/6)+2πn, n ∈ Z cм. рис. (π/24)+(π/2)n ≤ x ≤ (11π/24)+(π/2)n, n ∈ Z