SOLUTION: I am having some trouble graphing this eqaution: y=x^2-2x-8 The question asks that I find the y and x intercepts and the vertex. I got the x intercepts at 4 and-2, the y intercept

Algebra ->  Graphs -> SOLUTION: I am having some trouble graphing this eqaution: y=x^2-2x-8 The question asks that I find the y and x intercepts and the vertex. I got the x intercepts at 4 and-2, the y intercept      Log On


   

Question 144744: I am having some trouble graphing this eqaution: y=x^2-2x-8
The question asks that I find the y and x intercepts and the vertex. I got the x intercepts at 4 and-2, the y intercept at 0,-8 and the vertex at -1,-7. The vertex doesnt seem to work though. I'd appreciate any help I could get.
~Kyle
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Everything is correct except for the vertex


To find the vertex, we first need to find the axis of symmetry (ie the x-coordinate of the vertex)
To find the axis of symmetry, use this formula:

x=-b%2F%282a%29

From the equation y=x%5E2-2x-8 we can see that a=1 and b=-2

x=%28--2%29%2F%282%2A1%29 Plug in b=-2 and a=1


x=2%2F%282%2A1%29 Negate -2 to get 2


x=%282%29%2F2 Multiply 2 and 1 to get 2



x=1 Reduce


So the axis of symmetry is x=1


So the x-coordinate of the vertex is x=1. Lets plug this into the equation to find the y-coordinate of the vertex.


Lets evaluate f%281%29

f%28x%29=x%5E2-2x-8 Start with the given polynomial


f%281%29=%281%29%5E2-2%281%29-8 Plug in x=1


f%281%29=%281%29-2%281%29-8 Raise 1 to the second power to get 1


f%281%29=-9 Now combine like terms


So the vertex is (1,-9)



So let's use the this (along with the other pieces you solved for) to graph y=x%5E2-2x-8
Graph of y=x%5E2-2x-8