Răspuns:
Explicație pas cu pas:
ΔBEC - ∡E=90 °( BE⊥CD)
-BE= 8 cm
-∡C=45°
↓
∡BEC =180-90-45 =45 °→ΔBEC= isoscel ∡EC= 8 cm
↓
DC= DE +EC →DC=20+ 8 →DC= 28 cm
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8)
CE ⊥AD →∡E=90°
ΔCED -∡ E=90
-∡C= 30
- CD= 10 cm
↓
Conform teoremei ∡de 30 °
↓
CE =10:2=5 cm
AB=CE →AB =5 cm