a. Ta có: a//b
Mà \(a\perp c\)
\(\Rightarrow b\perp c\)
b. Ta có: a//b
=> \(\widehat{B_2}=\widehat{A_4}=45^0\) (2 góc so le trong)
Ta có: \(\widehat{B_1}+\widehat{B_2}=180^0\) (2 góc kề bù)
\(\Rightarrow\widehat{B_1}=180^0-\widehat{B_2}=180^0-45^0=135^0\)
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