Ta có:
`hat\{B}-hat\{C}=20^0`
`=>hat\{B}=20^0 +C`
Ta có:
`hat\{A}+hat\{B}+hat\{C}=180^0`
`=>120^0 + 20^0 +hat\{C}+hat\{C}=180^0`
`=>2.hat\{C}=180^0-140^0`
`=>2.hat\{C}=40^0`
`=>hat\{C}=40^0 :2=20^0`
Vì `hat\{B}-hat\{C}=20^0`
`=>hat\{B}=20^0 + hat\{C}`
`=>hat\{B}=20^0+20^0=40^0`
Vậy `hat\{B}=40^0` ` và ` `hat\{C}=20^0`