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Answer:
a) x = -1, x = 4
b) y = x^2 -3x -4
Explanation:
a) We observe the x-intercepts are x = -1 and x = 4. These are the solutions to y = 0, which is usually what we want in cases like this.
The solutions are x=-1 and x=4.
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b) We know two of the factors are (x +1) and (x -4). There may be an additional constant factor for vertical scaling. One point we can check is the y-intercept.
y = a(x +1)(x -4)
For x=0, this is ...
y = a(1)(-4) = -4a
The y-intercept is y = -4, so we have a=1.
The factored equation is ...
y = (x +1)(x -4)
Multiplying this out gives the equation in standard form:
y = x^2 -3x -4
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Additional comment
Your teacher may want the standard form equation to be ...
x^2 -3x -4 = 0
This is the equation of two specific points: x=-1 and x=4. It is not the equation of the graph.