In Fig. 6.9, BC = CA and ∠A = 40°. Then, ∠ACD is equal to
(a) 40°
(b) 80°
(c) 120°
(d) 60°
Isosceles: ∠B = ∠C = 70°. Exterior ∠ACD = 180° – 100° = 80°.