Points c and d divide the semicircle into three equal parts. match the angles with their measures.

∠cae
a. ∠cad
b. ∠bae
c. ∠dec
d. 15°
e. 30°
f. 60°
g. 120°
h. 180°

∠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°.

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