SOLUTION: 5b. What three techniques can be used to solve a quadratic equation? Demonstrate these techniques on the equation "12x2 - 10x - 42 = 0." I appreciate your help, thank you.

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: 5b. What three techniques can be used to solve a quadratic equation? Demonstrate these techniques on the equation "12x2 - 10x - 42 = 0." I appreciate your help, thank you.      Log On


   



Question 182674: 5b.

What three techniques can be used to solve a quadratic equation? Demonstrate these techniques on the equation "12x2 - 10x - 42 = 0."
I appreciate your help, thank you.

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
What three techniques can be used to solve a quadratic equation? Demonstrate these techniques on the equation "12x2 - 10x - 42 = 0."
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This is well covered by the onsite solver.
As an example 6x%5E2+-+5x+-+21+=+0
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 6x%5E2%2B-5x%2B-21+=+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=%28-5%29%5E2-4%2A6%2A-21=529.

Discriminant d=529 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--5%2B-sqrt%28+529+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-5%29%2Bsqrt%28+529+%29%29%2F2%5C6+=+2.33333333333333
x%5B2%5D+=+%28-%28-5%29-sqrt%28+529+%29%29%2F2%5C6+=+-1.5

Quadratic expression 6x%5E2%2B-5x%2B-21 can be factored:
6x%5E2%2B-5x%2B-21+=+%28x-2.33333333333333%29%2A%28x--1.5%29
Again, the answer is: 2.33333333333333, -1.5. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+6%2Ax%5E2%2B-5%2Ax%2B-21+%29

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2 methods are covered, the quadratic equation and factoring. (The solver gets the factors wrong if the coeff of the x^2 is not 1.)
The 3rd method is completing the square. Once you know the quadratic equation, use it and forget about completing the square.
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Graphical solutions might be a 4th method.