Đáp án:
Vì $AB//CD$
` => \hat{A} + \hat{D} = 180^0`
Mà ` \hat{A} - \hat{D} = 20^0`
` => \hat{A} = ( 180^0 +20^0 ) : 2 = 100^0`
` => \hat{D} = 100^0 -20^0 = 80^0`
Mà `\hat{B} + \hat{C} = 180^0`
` \hat{B} = 2 \hat{C} `
` => 3 \hat{C} = 180^0`
` => \hat{C} = 180^0 : 3 = 60^0`
` => \hat{B} = 2* 60^0 = 120^0`
Vậy `\hat{A} = 100^0 ; \hat{B} = 120^0 ; \hat{C} = 60^0 ; \hat{D} = 80^0`