a: Ta có: a\(\perp\)c
b\(\perp\)c
Do đó: a//b
b: Ta có: \(\widehat{A_1}+\widehat{A_2}=180^0\)(hai góc kề bù)
=>\(\widehat{A_2}=180^0-45^0=135^0\)
Ta có: a//b
=>\(\widehat{A_2}=\widehat{B_1}\)(hai góc so le trong)
=>\(\widehat{B_1}=135^0\)
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