Question 610832
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Hi, 
As to remembering..it might help to remember WHAT a particular form easily tell us:
Hope this helps. 
For ex:
 y = x^2 - 6x +8   this tells us the y-intercept when x = 0 is (0,8)
factored: y = (x-4)(x-2) esily gives us the zeros of the functions (when y = 0)
          0 = (x-4)(x-2) says x= 4 and x =2 are  the x-intercepts
vertex form:  y = (x-3)^2 -9 + 8  OR  y = 1·(x-3)^2 -1 
                                    says Vertex is (3,-1)& as 1>0, parabola opens Upward
We know the graph looks like this:
{{{drawing(300,300,   -10,10,-10,10,  
 grid(1),
circle(3, -1,0.4),
graph( 300, 300, -10,10,-10,10,0,x^2 - 6x +8 ))}}}