SOLUTION: Use the quadratic formula to solve the quadratic equation x^2 − 8x − 4 = 0.

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Question 751680: Use the quadratic formula to solve the quadratic equation x^2 − 8x − 4 = 0.
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 1x%5E2%2B-8x%2B-4+=+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%2A1%2A-4=80.

Discriminant d=80 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--8%2B-sqrt%28+80+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-8%29%2Bsqrt%28+80+%29%29%2F2%5C1+=+8.47213595499958
x%5B2%5D+=+%28-%28-8%29-sqrt%28+80+%29%29%2F2%5C1+=+-0.47213595499958

Quadratic expression 1x%5E2%2B-8x%2B-4 can be factored:
1x%5E2%2B-8x%2B-4+=+1%28x-8.47213595499958%29%2A%28x--0.47213595499958%29
Again, the answer is: 8.47213595499958, -0.47213595499958. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B-8%2Ax%2B-4+%29