Đáp án+Giải thích các bước giải:
Ta có:
`\hat{A}+\hat{B}+\hat{C}+\hat{D}=360^o` (Tổng các góc trong `1` tứ giác)
`⇒\hat{A}+\hat{A}+10^o +\hat{B}+10^o +\hat{C}+10^o=360^o`
`⇒2\hat{A}+30^o +\hat{A}+10^o +\hat{B}+10^o=360^o`
`⇒3\hat{A}+50^o +hat{A}+10^o=360^o`
`⇒4\hat{A}+60^o=360^o`
`⇒4\hat{A}=300^o`
`⇒\hat{A}=75^o`
`\hat{B}=\hat{A}+10^o=75^o +10^o=85^o`
`\hat{C}=\hat{B}+10^o=85^o +10^o=95^o`
`\hat{D}=\hat{C}+10^o=95^o +10^o=105^o`
`→A`
