properties of circle
2012-09-20 9:10 pm
回答 (1)
2012-09-20 9:33 pm
✔ 最佳答案
Join AE , ∠EAF = ∠BAC = 30° (equal arcs, equal ∠s) ∠CAE + ∠CDE = 180° (opp. ∠s, cyclic quad.)
(a - ∠EAF) + b = 180°
(a - 30°) + b = 180°
a + b = 210°
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