## Thinking Mathematically (6th Edition)

$m\angle{HAB}= 160^o$ $\angle{HAB}$ is obtuse.
point H is at $180^o$ point B is at $20^o$ Thus, $m\angle{HAB} =180^o-20^o=160^o$ Obtuse angles are angles whose measure is more than 90 degrees but less than 180 degrees. Thus, $\angle{HAB}$ is obtuse.