Question 683283
y = 3x^2+12x+20


y - 20 = 3x^2+12x


y - 20 = 3(x^2+4x)


y - 20 = 3(x^2+4x+4-4)


y - 20 = 3((x^2+4x+4)-4)


y - 20 = 3((x+2)^2-4)


y - 20 = 3(x+2)^2-3*4


y - 20 = 3(x+2)^2-12


y = 3(x+2)^2-12+20


y = 3(x+2)^2 + 8


===================================================================


So after completing the square, 


3x^2+12x+20


turns into 


3(x+2)^2 + 8


which is now in vertex form.