选 A, C, D。
x^9 = 1 = cos0 + isin0,
x = cos[(0+2kπ)/9]+ isin[(0+2kπ)/9] = cos(2kπ/9)+ isin(2kπ/9)
k = 0, 1, 2, 3, 4, 5, 6, 7, 8
得 x1 = 1 是一个复根(复数包含实数), 选 A;
x2 = cos(2π/9)+ isin(2π/9) = cos(40°) + isin(40°) , 是一个复根, 选 D;
x3 = cos(4π/9)+ isin(4π/9)
x4 = cos(2π/3)+ isin(2π/3)
x5 = cos(8π/9)+ isin(8π/9)
x6 = cos(10π/9)+ isin(10π/9)
x7 = cos(4π/3)+ isin(4π/3) = - 1/2 - i√3/2, 是一个复根, 选 C;
x8 = cos(14π/9)+ isin(14π/9)
x9 = cos(16π/9)+ isin(16π/9)
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