Posted by **Nancy** on Sunday, March 29, 2009 at 9:49pm.

What is the relationship between the

x-intercepts of a parabola and its vertex's x-coordinate?

- Algebra 1- 8th Grade -
**Reiny**, Sunday, March 29, 2009 at 9:53pm
if you average the x-intercepts , you get the x coordinate of the vertex.

y = x^2 - 2x - 8

= (x-4)(x+2)

so the x intercepts are 4 and -2

average of those = (-2 + 4)/2 = 1

so the vertex is (1, ...)

- Algebra 1- 8th Grade -
**Nancy**, Sunday, March 29, 2009 at 10:02pm
If I were to write down:

"When you find the median between the two intercepts, it is the x-intercept of the vertex."

do you think that's a true relationship still ?

- Algebra 1- 8th Grade -
**Reiny**, Sunday, March 29, 2009 at 10:36pm
I would use the word "mean"

"Mean" is what is known as the average in everyday language, "median" is the middle value of a set of data.

Of course if you only have two data values, as the x-intercepts, it actually does not matter.

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