`#Sad`
`\text{Vì}` `{(a \bot c),(b \bot c):}`
`⇒` `a //// b`
`\text{Ta có:}`
`+)` `\hat{B1}+\hat{B2} = 180^o` `\text{(kề bù)}`
`⇒` `\hat{A2} = 290^o-180^o = 110^o`
`+)` `\hat{A1}+\hat{A2} = 180^o` `\text{(kề bù)}`
`⇒ \hat{A1} = 180^o-110^o = 70^o`
`+)` `\hat{A1} = \hat{A3}` `\text{(đối đỉnh)}`
`⇒ \hat{A3} = 70^o`
`\text{Vì}` `a //// b`
`+)` `\hat{A1} = \hat{B2}` `\text{(so le trong)}`
`⇒ \hat{B2} = 70^o`
`+)` `\hat{B1}+\hat{B2} = 180^o` `\text{(kề bù)}`
`⇒ \hat{B1} = 180^o-70^o = 110^o`