SOLUTION: We are studying for a test on Quadratic equations. Equation is: 2x^2+4x-6=0 Why if the Discriminant is -b (plus or minus) square root of b^2-4ac/2Xa does Algebra.com solve it as

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Question 253942: We are studying for a test on Quadratic equations.
Equation is: 2x^2+4x-6=0
Why if the Discriminant is -b (plus or minus) square root of b^2-4ac/2Xa does Algebra.com solve it as -4 (plus or minus) square root of 4^2+4x2x(-6)/2x2
What does the +or- mean? Is there a clear explanation? For instance, when does it change a numeric in the square root equation; what is the rule?
Thanks, Shawn G
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
The discriminant is:
b%5E2+%2B+4ac
-----------------
This is well covered by the onsite solver.
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 2x%5E2%2B4x%2B-6+=+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%2A2%2A-6=64.

Discriminant d=64 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-4%2B-sqrt%28+64+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%284%29%2Bsqrt%28+64+%29%29%2F2%5C2+=+1
x%5B2%5D+=+%28-%284%29-sqrt%28+64+%29%29%2F2%5C2+=+-3

Quadratic expression 2x%5E2%2B4x%2B-6 can be factored:
2x%5E2%2B4x%2B-6+=+%28x-1%29%2A%28x--3%29
Again, the answer is: 1, -3. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+2%2Ax%5E2%2B4%2Ax%2B-6+%29