SOLUTION: how to find the equation of line of symmetry for y=9-8x-x^2 i have tried by using the completiing the square method and got the answer in surd form. my answer is 4 root 7.

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Question 204373: how to find the equation of line of symmetry for y=9-8x-x^2
i have tried by using the completiing the square method and got the answer in surd form. my answer is 4 root 7.
Answer by ichudov(507) About Me  (Show Source):
You can put this solution on YOUR website!
Try graphing it:
graph+%28+800%2C+600%2C+-10%2C+1%2C+-10%2C+30%2C+9-8x-x%5E2+%29+
That would give you some idea.
Then you can solve quadratic equation and note that the line of symmetry is between roots::
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case -1x%5E2%2B-8x%2B9+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%28-8%29%5E2-4%2A-1%2A9=100.

Discriminant d=100 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--8%2B-sqrt%28+100+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-8%29%2Bsqrt%28+100+%29%29%2F2%5C-1+=+-9
x%5B2%5D+=+%28-%28-8%29-sqrt%28+100+%29%29%2F2%5C-1+=+1

Quadratic expression -1x%5E2%2B-8x%2B9 can be factored:
-1x%5E2%2B-8x%2B9+=+-1%28x--9%29%2A%28x-1%29
Again, the answer is: -9, 1. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+-1%2Ax%5E2%2B-8%2Ax%2B9+%29