SOLUTION: What is the Y coordinate of the vertex for the quadratic: y = x^2 -8x -9 Please show your work Thank you

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: What is the Y coordinate of the vertex for the quadratic: y = x^2 -8x -9 Please show your work Thank you      Log On


   

Question 737763: What is the Y coordinate of the vertex for the quadratic: y = x^2 -8x -9
Please show your work
Thank you
Found 2 solutions by Susan-math, MathLover1:
Answer by Susan-math(40) About Me  (Show Source):
You can put this solution on YOUR website!
Find x=-b%2F%282a%29=-%28-8%29%2F%28%282%281%29%29%29=4
then substitute that for x to find the corresponding y:
So y+=+%284%29%5E2=8%284%29-9=-25

Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!
y+=+x%5E2+-8x+-9..first write it in vertex form y=%28h-h%29%5E2%2Bk where h and k are x and y coordinates of vertex
y+=+x%5E2+-8x+-9%7D%7D.....add+and+subtract+%7B%7B%7B16
y+=+x%5E2+-8x%2B16-16+-9%7D%7D....group%0D%0A%0D%0A%7B%7B%7By+=+%28x%5E2+-8x%2B16%29-16+-9...complete the square
y+=+%28x+-4%29%5E2-16+-9
y+=+%28x+-4%29%5E2-25
so, h=4 and -25
y coordinate of vertex is -25
see it on a graph: