Answer:
C) one half the measure of their intercepted arcs; m arc CDE= 2 ⋅ m∠CFE and arc CFE= 2 ⋅ m∠CDE
Step-by-step explanation:
Quadrilateral CDEF is inscribed in circle A, so:
m arc CDE + m arc CFE= 360°.
∠CFE and ∠CDE are inscribed angles, which means that their measures are <u>one half the measure of their intercepted arcs.</u><u> </u>
So, <u>m arc CDE= 2 ⋅ m∠CFE and arc CFE= 2 ⋅ m∠CDE. </u>
Using the substitution property of equality:
2 ⋅ m∠CFE + 2 ⋅ m∠CDE = 360°.
Using the division property of equality, divide both sides of the equation by 2, resulting in:
m∠CFE + m∠CDE = 180°.
Therefore, ∠CFE and ∠CDE are supplementary.
The correct option is C.