SOLUTION: I need help with this problem of finding the x intercepts. y = x^2 + 4x -1

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Question 173144: I need help with this problem of finding the x intercepts.
y = x^2 + 4x -1
Found 2 solutions by Alan3354, stanbon:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
I need help with this problem of finding the x intercepts.
y = x^2 + 4x -1
-----------------
At the x-intercepts, y is zero.
y = x^2 + 4x -1 = 0
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 1x%5E2%2B4x%2B-1+=+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=%284%29%5E2-4%2A1%2A-1=20.

Discriminant d=20 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-4%2B-sqrt%28+20+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%284%29%2Bsqrt%28+20+%29%29%2F2%5C1+=+0.23606797749979
x%5B2%5D+=+%28-%284%29-sqrt%28+20+%29%29%2F2%5C1+=+-4.23606797749979

Quadratic expression 1x%5E2%2B4x%2B-1 can be factored:
1x%5E2%2B4x%2B-1+=+%28x-0.23606797749979%29%2A%28x--4.23606797749979%29
Again, the answer is: 0.23606797749979, -4.23606797749979. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B4%2Ax%2B-1+%29

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
finding the x intercepts.
y = x^2 + 4x -1
x^2 + 4x -1 = 0
x = [-4 +- sqrt(16 - 4*1*-1)]/2
x = [-4 +- sqrt(20)]/2
x = [-4 +-2sqrt(5)]/2
x = [-2 +-sqrt(5)]
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Cheers,
Stan H.