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Question 135329: Use the graph of y=x^2-2x-8, does this function have a maximum and minimum and if so what are they?
Answer by Earlsdon(6294)   (Show Source):
You can put this solution on YOUR website! Does the graph of: have a maximumum and minimum?
Well, it may have a maximum or it may have a minimum, but it doesn't have both!
The graph of a quadratic equation ( ), such as this, is called a "parabola" and a parabola has a maximum or a minimum depending upon whether it opens upwards (has a minimum) or opens downwards (has a maximum).
You can tell which way the parabola opens by inspecting the coefficient of the  term, which is +1 in your problem.
If this coefficient is positive, then the parabola opens upwards and the graph has a minimum.
If the coefficient is negative,then the parabola opens downwards and the graph has a maximum.
The maximum/minimum point (also known as the "vertex") can be found as follows:
The x-coordinate of this point is:
 The a is the coefficient of the term and the b is the coefficient of the  term.
In your equation, a = 1 and b = -2, so...
 This is the x-coordinate of the vertex.
To find the y-coordinate, substitute x = 1 into the given quadratic equation and solve for y:
Substitute x = 1.
The vertex (or the minimum in this case) is at (1, -9)
Let's see what the graph looks like:
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