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 . So, . 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. twice the measure of their intercepted arcs; 2 ⋅ m arc CDE= m∠CFE and 2 ⋅ arc CDE = m∠CDE twice the measure of their intercepted arcs; marc CDE= 2 ⋅ m∠CFE and arc CFE = 2 ⋅ m∠CDE one half the measure of their intercepted arcs; m arc CDE= 2 ⋅ m∠CFE and arc CFE= 2 ⋅ m∠CDE one half the measure of their intercepted arcs; 2 ⋅ m arc CDE= m∠CFE and 2 ⋅ arc CFE= m∠CDE