∠CAE = 120°
∠CAD = 60°
∠BAE = 180°
∠DEC = 30°
We start out with the fact that points C and D split the semicircle into 3 sections. This means that ∠BAC, ∠CAD and ∠DAE are all 60° (180/3 = 60).
Since it forms a straight line, ∠BAE is 180°.
Since it is formed by ∠CAD and ∠DAE, ∠CAE = 60+60 = 120°.
We know that an inscribed angle is 1/2 of the corresponding arc; since CD is 1/3 of the circle, it is 1/3(180) = 60; and this means that ∠DEC = 30°.
