\(ABCD\) là hình bình hành
\(\Rightarrow\left\{{}\begin{matrix}\widehat{DAB}=\widehat{BCD}\\\widehat{ADC}=\widehat{ABC}\end{matrix}\right.\)
AB // CD
\(\Rightarrow\widehat{BAD}+\widehat{ADC}=180^0\)
Hay \(60^0+\widehat{ADC}=180^0\)
\(\Rightarrow\widehat{ADC}=180^0-60^0=120^0\)
mà \(\widehat{ADC}=\widehat{ABC}\) \(\Rightarrow\widehat{ABC}=120^0\)
Vậy số đo các góc : \(\widehat{ABC}=120^0;\widehat{BCD}=60^0;\widehat{CDA}=120^0\)
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