a) Ta có $a\perp HK, b\perp HK $ nên a//b.
b) Ta có a//b suy ra $\widehat{ABH}=\widehat{BAb}=55^{\circ}$ (hai góc so le trong)
a) Ta có $a\perp HK, b\perp HK $ nên a//b.
b) Ta có a//b suy ra $\widehat{ABH}=\widehat{BAb}=55^{\circ}$ (hai góc so le trong)