Thursday
May 5, 2016

# Homework Help: Algebra 1- 8th Grade

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.