Question

In figure BC = CA and ∠A = 40°. Then ∠ACD is...
a)40° b) 80° c) 120° d) 60°

Answer 1

b. 80°

Explanation:

B is 40°

A triangle has 180°

40 + 40 + x = 180

80 + x = 180

x = 100

Since it's a supplementary angle...

180 - 100 = 80

Answer 2

B

Explanation:

The size of the exterior angle in a triangle is the sum of interior opposite angles. In this case, it's

Angle ACD=40+40=80° (Exterior angle=sum of int. opp. angles)