你答案的错误是没有把 前面的 1当成复数的一部分
z = a + b i
令 r=√a²+b², tan t = b/a 且 a,b的符号确定t所在象限
z =r(a/r + b/r i) = r e^(i t)
所以你的例子: 1-cos(π/5) + i sin(π/5)
r² = (1-cos(π/5))²+(sin(π/5))² = 2-2 cos(π/5)=4sin(π/10)²
r = 2 sin(π/10),a>0,b>0,所以t第一象限
t = arcsin( sin(π/5)/(2 sin(π/10)))=arcsin( cos(π/10)) = π/2 - π/10 = 2π/5
因此 z = 2 sin(π/10) e^(2π i / 5)