Xét tứ giác OINJ có \(\widehat{O}=90^o,\widehat{I}=90^o,\widehat{J}=90^o\)
\(\Rightarrow\widehat{N}=360^o-\left(90^o+90^o+60^o\right)\)
= \(90^o\)
Xét tam giác INJ
có \(\widehat{I_2}=\widehat{I_3}=30^o,\widehat{N}=90^o\)
\(\Rightarrow\widehat{J_2}=\widehat{J_1}=180^o-\left(30^o+90^o\right)=60^o\)
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