SOLUTION: 9x^2+21x-8=0

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Question 572378: 9x^2+21x-8=0
Answer by Maths68(1474) About Me  (Show Source):
You can put this solution on YOUR website!
9x%5E2%2B21x-8=0
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 9x%5E2%2B21x%2B-8+=+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=%2821%29%5E2-4%2A9%2A-8=729.

Discriminant d=729 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-21%2B-sqrt%28+729+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%2821%29%2Bsqrt%28+729+%29%29%2F2%5C9+=+0.333333333333333
x%5B2%5D+=+%28-%2821%29-sqrt%28+729+%29%29%2F2%5C9+=+-2.66666666666667

Quadratic expression 9x%5E2%2B21x%2B-8 can be factored:
9x%5E2%2B21x%2B-8+=+9%28x-0.333333333333333%29%2A%28x--2.66666666666667%29
Again, the answer is: 0.333333333333333, -2.66666666666667. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+9%2Ax%5E2%2B21%2Ax%2B-8+%29