SOLUTION: Here is the problem: y=-2x^2+8x-5 Here is what I tried: h=-(8/2(-2)) -2(2)^2-8(2)-5 -8-16-5 ... This doesn't make sense, because the y value seems too large. Am I doing th

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: Here is the problem: y=-2x^2+8x-5 Here is what I tried: h=-(8/2(-2)) -2(2)^2-8(2)-5 -8-16-5 ... This doesn't make sense, because the y value seems too large. Am I doing th      Log On


   

Question 172109: Here is the problem: y=-2x^2+8x-5
Here is what I tried:
h=-(8/2(-2))
-2(2)^2-8(2)-5
-8-16-5
...
This doesn't make sense, because the y value seems too large.
Am I doing this problem correctly?
Thanks!
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Here is the problem: y=-2x^2+8x-5
Here is what I tried:
h=-(8/2(-2))
-2(2)^2-8(2)-5
-8-16-5
...
This doesn't make sense, because the y value seems too large.
Am I doing this problem correctly?
-----------------
I think you want to find the values of x in:
-2x^2+8x-5 = 0
If so:
2x^2-8x+5 = 0
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 2x%5E2%2B-8x%2B5+=+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%2A2%2A5=24.

Discriminant d=24 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--8%2B-sqrt%28+24+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-8%29%2Bsqrt%28+24+%29%29%2F2%5C2+=+3.22474487139159
x%5B2%5D+=+%28-%28-8%29-sqrt%28+24+%29%29%2F2%5C2+=+0.775255128608411

Quadratic expression 2x%5E2%2B-8x%2B5 can be factored:
2x%5E2%2B-8x%2B5+=+%28x-3.22474487139159%29%2A%28x-0.775255128608411%29
Again, the answer is: 3.22474487139159, 0.775255128608411. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+2%2Ax%5E2%2B-8%2Ax%2B5+%29

Ignore the factors, it's not right. The answers are:
2+sqrt(6)/2
2=sqrt(6)/2