The real converted into complex by using Euler's formula,complex form of Fourier series was gained. And defined its inner spaces and normed spaces, the polarization identity for inner spaces and operators and approximation theorem of complex Fourier series were gained.%主要通过Euler公式进行实复转换,得到复形式Fourier级数,并定义其内积和范数,得到复Fourier级数内积及算子的极化恒等式和逼近定理.
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