Question 11

$$\overline{AB}$$ and $$\overline{CD}$$ are chords of a circle such that $$\overrightarrow{BA}$$ and $$\overrightarrow{DC}$$ intersect in a point E outside the circle. F is a point on the minor arc BD such that $$\angle FAB = 22^\circ$$, $$\angle FCD = 18^\circ$$. Then $$\angle AEC + \angle AFC$$ (in degrees) = _________.


Correct Answer: 40

Solution

Inscribed angles give arc $$FB = 2 \times 22^\circ = 44^\circ$$ and arc $$FD = 2 \times 18^\circ = 36^\circ$$, so arc $$BD = 80^\circ$$. For the secants from E, $$\angle AEC = \frac{\text{arc } BD - \text{arc } AC}{2}$$, and $$\angle AFC = \frac{\text{arc } AC}{2}$$. Adding, $$\angle AEC + \angle AFC = \frac{\text{arc } BD}{2} = 40^\circ$$.

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