`a)` Ta có: `AE////BC`
\(\Rightarrow\widehat{y}=\widehat{EAB}=70^o\) ( so le trong )
\(\widehat{x}+\widehat{y}+\widehat{ACB}=180^o\) ( tổng 3 góc )
\(\Rightarrow\widehat{x}=180^o-70^o-75^o=35^o\)
`b)`Ta có: `AE////BC`
\(\Rightarrow\widehat{y}=\widehat{EAC}=60^o\) ( so le trong )
\(\widehat{x}+\widehat{y}+\widehat{ABC}=180^o\) ( tổng 3 góc )
\(\Rightarrow\widehat{x}=180^o-60^o-90^o=30^o\)