- cos ( 1/2 x + 1/5 π ) = 0 ( and because if cos α = 0, α= π/2 + k π, k ∈ Z ) 1/2 x + π/5 = π/2 + k π, k ∈ Z 1/2 x = π/2 - π/5 + k π / * 2 x = π - 2π/5 + 2 k π x = 3/5 π + 2 k π = 0.6 π + 2 k π Answer: If k = 0: x 1 = 0.6 π = 3π/5 k = 1 : x 2 = 2.6 π = 13π/5
