A function whose graph is symmetrical about the origin must be odd.(3x + 3–x) is an even function.Since cos x is an even function and log⁡x+1+x2 is an odd function,∴cos⁡log⁡x+1+x2 is an even function.If f (x + y) = f (x) + f (y) ∀ x, y ∈ R, then f (x) must be odd.