4. a ) Daca M ∈ bisectoarei ( ∡ XOY) => d( M;OX) = d ( M;OY)
=> MA = MB => MC = MD => AC = BD
b) m (∡ OAM) = m (∡ MBO ) = 90°
Si cum MA = MB
=> OAMB - patrat
=> OM ⊥ AB
5. a ) Δ EBO ≡ Δ OFC pt. ca - m ( ∡ BOE) = m( ∡ COF) (opuse la varf)
- BO≡ OC
=> BE ≡ FC
b) BE ⊥ AO
CF⊥AO
=> CF ║ BE
Si cum BE = FC
=> BECF - paralelogram => BF = CE
