Solution: Let this parabolic equation be y=ax2+bx+c, and the abscissa of the parabola vertex is-2a/B. Because P (-2,3) is its vertex, -2a/b =-2, and b=4a. Substituting p (-2,3) into the equation is 3=4a-2b+c, because b =-4a+c and 0=-3a+c, a=-3 and c=-9, so b=- 12, so the equation is.

y=-3x2- 12x-9