In △BAD and △BAC,
AB=AB
∠BAD=∠BAC=90
AD=AC
∴△BAD≌△BAC(SAS)
∴BD=BC
Page 15: 3. In △ABE and △ACD,
AB=AC
∠A=∠A
AE=AD
∴△ABE≌△ACD
4. just measure the distance of A'B'
Reason: ∫ Point O is the midpoint between AA' and BB'.
∴ao=a′o
BO = B′O
In △AOB and △ a ′ ob ′.
AO = A′O
∠AOB =∠A′OB′
BO = B′O
∴△aob≌△a′ob′
∴a′b′=ab