`#Mon`
`a)\text{ Ta có:}` `\hat{BAx}+\hat{BAC}=180^o(\text{ 2 góc kề bù})`
`<=>\hat{BAC}=180^o-\hat{BAx}`
`<=>\hat{BAC}=180^o-115^o`
`<=>\hat{BAC}=65^o`
`\text{ Ta lại có:}` `\hat{ACB}+\hat{CBA}+\hat{BAC}=180^o`
`<=>\hat{ACB}=180^o-(\hat{CBA}+\hat{BAC})`
`<=>\hat{ACB}=180^o-(75+65)`
`<=>\hat{ACB}=180^o-140^o`
`<=>\hat{ACB}=40^o`