The number of obtuse angles in Fig. 2.9 is
Obtuse angles are the angles which are greater than 90° and less than 180°.
so here individually none of them is an obtuse angle.
if we combine 20° and 45° still it is not and obtuse angle.
but, if combine 20° + 45° + 65°
then it is an obtuse angle.
also 20° + 45° + 65° + 30° is not an obtuse angle since its equal to 180°.
Similarly, 65 + 30 and 45 + 65 + 30 are also obtuse.
and 45° + 65° is also obtuse.
∴ 4 angles are obtuse