The correct option is B AC2=2.BC.DC.
In △ADB,
AB2=AD2+DB2 (By Pythagoras Theorem)
or AD2=AB2−DB2
In △ADC
AC2=AD2+DC2 (By Pythagoras Theorem)
Now, AC2=AB2−DB2+(DB+BC)2
AC2=AB2−DB2+DB2+BC2+2DB.BC
AC2=BC2+BC2+2DB.BC (Since, AB=BC)
AC2=2BC2+2DB.BC
AC2=2BC.(BC+DB)
AC2=2BC.DC