O1ˆ=2O2ˆO1^=2O2^
Mà Oˆ1+Oˆ2=1800O^1+O^2=1800 ( kề bù )
⇒3Oˆ2=1800⇒Oˆ2=1800:3=600⇒3O^2=1800⇒O^2=1800:3=600
⇒Oˆ1=600.2=1200⇒O^1=600.2=1200
⇒Oˆ1=Oˆ3=1200⇒O^1=O^3=1200 ( Đối đỉnh )
⇒Oˆ2=Oˆ4=600⇒O^2=O^4=600 ( đối đỉnh )
Ta có : \(\widehat{O_1}+\widehat{O_2}=180^0\)
Mà \(\widehat{O_1}=\frac{1}{2}\widehat{O_2}\)=> \(\widehat{O}_1=\frac{\widehat{O_2}}{2}\)
=> \(2\widehat{O_1}=\widehat{O_2}\)
=> \(2\widehat{O_1}+\widehat{O_1}=180^0\)
=> \(3\widehat{O_1}=180^0\)
=> \(\widehat{O_1}=60^0\)
Thế \(\widehat{O_1}=60^0\)vào ta có : \(60^0+\widehat{O_2}=180^0\)
=> \(\widehat{O_2}=120^0\)
Mà \(\widehat{O_1}\) và \(\widehat{O_3}\)đối đỉnh nên \(\widehat{O_1}=\widehat{O_3}=60^0\)
\(\widehat{O_2}=\widehat{O_4}=120^0\)đối đỉnh