Respuesta :

the vertex form of a parabola is 

y = a(x -h)^2 + k     where a is a constant and (h,k) is the vertex

so here we have 

y = a(x + 2)^2  - 20

when x = 0 y = -12  (from y-intercept) so:-

-12  = 4a - 20

4a = 8 
a = 2

so required equation is y = 2(x + 2)^2 - 20

convert to standard form

y = 2x^2 + 8x + 8 - 20

y = 2x^2 + 8x - 12