Solution: 1, let the analytical formula of parabola be y=a(x+ 1)(x-3), and substitute x=0 and y=3 to get a=- 1. So y=- x? +2x+3 .。

2. Parabolic vertex D( 1, 4), in △ AOC, AO= 1, CO=3. . AC= root 10. In delta △CBD. BC=3 2, CD= 2, BD=2 5, because AO/ CD=CO/BC=AC/BD, so △DBC∽△ACO.