Câu 5.
a//b => $\widehat{{{B}_{2}}}$ = $\widehat{{{A}_{1}}}$ = 70o (2 góc so le trong)
Có: $\widehat{{{B}_{1}}}$ + $\widehat{{{B}_{2}}}$ = 180o (2 góc kề bù)
=> $\widehat{{{B}_{1}}}$ = 180o - $\widehat{{{B}_{2}}}$ = 180o - 70o = 110o
a // b => $\widehat{{{D}_{2}}}$ = $\widehat{{{C}_{1}}}$ = 90o (2 góc đồng vị)
Có: $\widehat{{{D}_{1}}}$ + $\widehat{{{D}_{2}}}$ = 180o
=> $\widehat{{{D}_{1}}}$ = 180o - $\widehat{{{D}_{2}}}$ = 180o - 90o = 90o