Answer:
m(DE) = 90°
Step-by-step explanation:
Since both circles are equal, therefore, their radius would be equal too.
m<S = 180 - right angle (angles on a straight line)
m<S = 180 - 90 = 90°
m<R = m<S (congruent triangles)
m<R = 90°
m<R = m(DE) (central angle = intercepted arc based on the central angle theorem)
Substitute
90° = m(DE)
m(DE) = 90°
