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E ∈ [AC[
|CE| = b = |CD|
ΔCDE İkizkenar
|AB| = |AE| = a + b
ΔABD ∩ ΔADE = [AD]
|BD| = |DE|
∡BAD = ∡DAE
ΔABD ~ ΔADE (Kenar, Açı, Kenar)
∡CED = ∡ABD = 40° = ∡CDE
∡ACD = ∡CDE + ∡CED = 40° + 40° = 80°
∡BAC = 180° - 40° - 80° = 60°
x = 60° / 2 = 30°.