Câu 6.
Ta có: a $\bot$ c; a $\bot$ c => a //b (từ vuông góc đến song song)
Có: $\widehat{{{B}_{1}}}+\widehat{{{B}_{2}}}={{180}^{o}}$ (2 góc kề bù)
=> $\widehat{{{B}_{2}}}$ = ${{180}^{o}}$ - $\widehat{{{B}_{1}}}$ = ${{180}^{o}}$ - ${{130}^{o}}$ = ${{50}^{o}}$
Vì a // b nên $\widehat{{{A}_{1}}}= \widehat{{{B}_{2}}}$ (2 góc đồng vị) => $\widehat{{{A}_{1}}}$ = 50o