Ta có: `\hatA+\hatB+\hatC=180^@`
`<=>60^@+\hatB+50^@=180^@`
`<=> \hatB=70^@`
`=>\hat(ABD)=\hat(CBD) = \hatB :2=35^@`
Xét `\Delta ABD`: `\hatA+\hat(ABD)+\hat(ADB)=180^@`
`<=> 60^@+35^@+\hat(ADB)=180^@`
`<=> \hat(ADB)=85^@`
Xét `\DeltaCBD`: `\hat(CDB)+\hat(CBD)+\hatC=180^@`
`<=>\hat(CDB)+35^@+50^@=180^@`
`<=>\hat(CDB)=95^@`
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