SOLUTION: solve. x^2+18x-4=0. Do I use the quadratic equation or do I factor this to solve it? Please and thank you for your help

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: solve. x^2+18x-4=0. Do I use the quadratic equation or do I factor this to solve it? Please and thank you for your help      Log On


   

Question 177883: solve.
x^2+18x-4=0. Do I use the quadratic equation or do I factor this to solve it?
Please and thank you for your help
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
solve.
x^2+18x-4=0. Do I use the quadratic equation or do I factor this to solve it?
Please and thank you for your help
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I don't see how it can be factored.
If the factors are not obvious, use the quadratic formula, it always works and is often useful in factoing.
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 1x%5E2%2B18x%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=%2818%29%5E2-4%2A1%2A-4=340.

Discriminant d=340 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-18%2B-sqrt%28+340+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%2818%29%2Bsqrt%28+340+%29%29%2F2%5C1+=+0.219544457292887
x%5B2%5D+=+%28-%2818%29-sqrt%28+340+%29%29%2F2%5C1+=+-18.2195444572929

Quadratic expression 1x%5E2%2B18x%2B-4 can be factored:
1x%5E2%2B18x%2B-4+=+%28x-0.219544457292887%29%2A%28x--18.2195444572929%29
Again, the answer is: 0.219544457292887, -18.2195444572929. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B18%2Ax%2B-4+%29

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So it's
-9 + sqrt(85)
-9 - sqrt(85)