Ta có: \(\widehat{xOn}=\widehat{xOy}-\widehat{yOn}\)
\(\widehat{yOm}=\widehat{xOy}-\widehat{mOx}\)
Mà : \(\widehat{yOn}=\widehat{mOx}=90^o\)
\(\widehat{xOy}\) chung
=> \(\widehat{xOn}=\widehat{mOy}\)
b)Ta có: \(\widehat{yOn}+\widehat{mOx}=90^o+90^o\)
\(\widehat{yOn}+\widehat{mOx}=180^o\)
mà \(\widehat{xOm}=\widehat{xOn}+\widehat{nOm}\)
\(\widehat{yOn}=\widehat{yOm}+\widehat{nOm}\)
=>\(\widehat{yOm}+\widehat{nOm}+\widehat{xOn}+\widehat{nOm}=180^o\)
Ta thấy \(\widehat{xOy}=\widehat{xOn}+\widehat{nOm}+\widehat{yOm}\)
=> \(\widehat{xOy}+\widehat{nOm}=180^o\)
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