The number of triangles in Fig. 2.17 is ______.

Their names are _______.

In Fig. 2.15, points A, B, C, D and E are collinear such that

AB = BC = CD = DE. Then

(a) AD = AB + ____

(b) AD = AC + ____

(c) mid-point of AE is ____

(d) midpoint of CE is _____

(e) AE = _____ × AB.

In Fig. 2.16,

(a) ∠AOD is a/an _____ angle

(b) ∠COA is a/an _____ angle

(c) ∠AOE is a/an _____ angle

Number of angles less than 180° in Fig. 2.17 is ______ and their names are __________.

The number of straight angles in Fig. 2.17 is _____.