Circles — Maths STD 9 — Question

Proof: $BA$ is the major arc and angle $ADB$ is the angle formed by it in the alternate segment.
Therefore $2\angle\text{ADB}=\text{m}(\text{arc BA})$
$\Rightarrow2\angle\text{ADB}=360-\text{m}(\text{arc AB})$
$\Rightarrow2\angle\text{ADB}=360-\angle\text{AOB}(\text{since}(\text{arc AB})=\text{angle AOB})$
$\Rightarrow2\angle\text{ADB}>360-180(\text{since}\angle\text{AOB}<180)$
$\Rightarrow\angle\text{ADB}>90^\circ$
$\Rightarrow\angle\text{ADB}$ is obtuse.