Why is 3 = a x (1)^2 x (-3)^2 in this step of the solution?

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The equation 3 = a x (1)^2 x (-3)^2 is derived by substituting x=0 into the expressions a(x+1)^2 and (x-3)^2, resulting in a(1)^2 and (-3)^2 respectively. The values x=0 and y=3 are confirmed by the graph, where the function intersects the y-axis at a y-value of 3. This substitution leads to the conclusion that the equation holds true. Additionally, -1 and 3 are identified as roots of multiplicity 2, as they are both roots of y(x)=0 and local minima of y'(x)=0. The discussion clarifies the relationship between the graph and the equation.
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I understand everything before and after this line but not sure how they actually came to that conclusion, many thanks.
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ax^4 + bx^3 + cx^2 + dx + 3
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Because they stated that x=0, therefor a(x+1)^2 becomes a(0+1)^2 = a(1)^2 and (x-3)^2 becomes (0-3)^2 = (-3)^2.

Note that the values of x=0 and y=3 come directly from the graph. You can see that the function (the squiggly line on the graph) is at a y-value of 3 when it crosses the y-axis, which corresponds to an x-value of 0. Therefor x=0 and y=3, which you just plug into the equation.
 
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Ahhhh I see it now, many thanks!
 
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For those that are wondering why -1 and 3 are roots of multiplicity 2, it is because from the graph we can see that they are roots of y(x)=0 but also they are local minima hence also roots of y'(x)=0.
 
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