Giup e vs a ;-; e can gap a

- Xét `ΔABC` có `hat{BAC} = 80^o`

`⇒ hat{ACB} + hat{ABC} = 180^o - 80^o = 100^o`

- Xét `ΔBIC` có:

`1/2hat{ACB} + 1/2hat{ABC} + hat{BIC} = 180^o`

`⇒ 1/2(hat{ACB} + hat{ABC}) + hat{BIC} = 180^o`

`⇒ 1/2. 100^o + hat{BIC} = 180^o`

`⇒ hat{BIC} = 180^o - 50^o`

`⇒ hat{BIC} = 130^o`

Vậy `hat{BIC} = 130^o`