a, Đặt \(\widehat{ABC}\) = \(\alpha \) thì \(\widehat{ADC}\) = \(\alpha \)
\(\widehat{BAD}\) = 180\(^{\circ}\) - \(\alpha \)
Ta có:
\(\widehat{CBE}\) = \(\widehat{CBA}\) + \(\widehat{ABE}\) = \(\alpha \) + 60\(^{\circ}\)
\(\widehat{CDF}\) = \(\widehat{CDA}\) + \(\widehat{ADF}\) = \(\alpha \) + 60\(^{\circ}\)
\(\widehat{EAF}\) = 360\(^{\circ}\) - \(\widehat{EAB}\) - \(\widehat{DAF}\) - \(\widehat{BAD}\)
...
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