Concept:Use the identity cosθ−sinθ=2cos(θ+4π) and then solve the cosine equation.Explanation:Given:cosθ−sinθ=1Rewrite using the standard identity:2cos(θ+4π)=1Divide both sides by 2:cos(θ+4π)=21We know that cosx=21 when x=2nπ±4π, n∈Z.Here, x=θ+4π.So,θ+4π=2nπ+4πorθ+4π=2nπ−4πSolving these gives:θ=2nπorθ=2nπ−2π,n∈ZAnswer:θ=2nπ−2πorθ=2nπ,n∈ZHence, the correct option is Option A.