in the diagram shown, abc is an equilateral triangle and acd is an
isosceles triangle. what is the value of angle adc?
(1) 30°
(2) 45°
(3) 60°
(4) 15°

30°

Step-by-step explanation:

Since ΔACD is isosceles with congruent sides AC = CD , then

∠ADC = ∠CAD

The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.

∠ACB is an exterior angle of ΔACD, hence

∠ACD + ∠CAD = 60° , thus

2 ∠ADC = 60 ( divide both sides by 2 )

∠ADC = 30°

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