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Properties of the function f(x) = cos x. Domain: D = R. Image: Imf = [-1,1]. Zero: x_0 = π/2 + kπ, k ∈ Z. Monotonicity: The function is monotonic on the intervals: strictly decreasing on the intervals [2kπ, π+2kπ] k ∈ Z; strictly increasing on the intervals [π+2kπ, 2π+2kπ], k ∈ Z. Injectivity: Function is not injective. Evennes or oddness: Even function. Period: Function is periodic. The period T = 2π.