Question

I am having trouble with this problem. I have done it several times and come up with two different answers. Can someone tell me what I am doing wrong?

Write the quadratic function in the form a(x-h)^2+k

y=x^2-2x-9
(x^2-2x)-9
(x^2+2x+1-1)-9
(x^2+2x+1)
answers
(x+1)^2 or x^2-2x-9=y

Answer 1

I believe you are missing k. Remember y = x^2-2x-9 and y = a(x-h)^2+k. What you have gotten for y is (x+1)^2. If you expand it, you'll see that it is x^+2x+1 which is not equal to x^2-2x-9. From your work which I believe is mostly correct but you made a tiny mistake. You pulled out -9 and -1, -10, from the original equation. That should be what you're missing. Even though you pulled them out they don't disappear into thin air ;/.

Answer 2

So.....
from your answer I need to add a -10 to (x+1)^2+2x+-10?