$\begin{array}{l}j)\, f(x) = y = \dfrac{\cos2x}{x}\\ Ta \,\,có:f(-x) = \dfrac{\cos2(-x)}{-x}\\ =\dfrac{\cos(-2x)}{-x}\\ =-\dfrac{\cos2x}{x} = -f(x)\\ \text{Vậy y là hàm lẻ}\\ m)\,f(x) = y = x\cot x + \cos x\\ Ta\,\,có:f(-x) = (-x)\cot(-x) + \cos(-x)\\ =-x.(-\cot x) + \cos x\\ = x\cot x + \cos x = f(x)\\ \text{Vậy t là hàm chẵn}\end{array}$