help iso question

[WrierJeffs]

question follows:

As shown in the figure below, ?ABC is isosceles with the length of AB equal to the
length of AC. The measure of ?A is 40° and points B, C, and D are collinear. What is
the measure of ?ACD ?
A
40°
B C D

my initial answer was 140 but was wrong, since it's a iso-triangel shouldn't it equal to 180?
answer is 110 but I want to know why.
help me please!!!!

 

[Loren]

The sum of the angles of a triangle is 180°. Angle A is 40. So angle B + angle C is how much? And since the opposite sides are equal, what can be said about angles B and C?

 

[garf]

the other angles of the triangle is 70. and like B, C, D they are colinear, therefore 180 - 70 = 110