Quadrilateral CDEF is inscribed in circle A. Which statements complete the proof to show that ∠CFE and ∠CDE are supplementary? Quadrilateral CDEF is inscribed in circle A. Quadrilateral CDEF is inscribed in circle A, so m arc CDE+ m arc CFE= 360°. ∠CFE and ∠CDE are , which means that their measures are . So, m arc CDE= 2 ⋅ m∠CFE and arc CFE = 2 ⋅ m∠CDE. 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. central angles; equal to the measure of their intercepted arcs inscribed angles; equal to the measure of their intercepted arcs central angles; one half the measure of their intercepted arcs inscribed angles; one half the measure of their intercepted arcs