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  1.分别在两个图中画出δ(n)和δ(n-2)，其中-10≤n≤10，画出U（n）其中-10≤n≤10。 2.分别在两个图中画出x1(n)=cos(2π×20×0.01×n)，0≤n≤10和x2(n)=(0.8)n，1≤n≤6。 3.由上一题，计算y(n)=x1(n)+x2(n)，并画图。(1. Draw the figure at two δ (n) and δ (n-2), where-10 ≤ n ≤ 10, draw the U (n) where-10 ≤ n ≤ 10. 2. Respectively in the two Draw the figure x1 (n) = cos (2π × 20 × 0.01 × n), 0 ≤ n ≤ 10 and x2 (n) = (0.8) n, 1 ≤ n ≤ 6. 3. from the previous question, calculate y (n) = x1 (n)+ x2 (n), and drawing.)