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Excel > Data Analysis > Goal Seek - Quadratic Equation | < Previous | Next > |
What are the two roots of a Quadratic Equation ? |
Lets suppose we have a quadradic equation and we want to find the roots. | ||
One way to find the roots is to use the Goal Seek. |
Create a simple Table |
You must first create a simple worksheet that contains the following information. | ||
This table can be used to solve any quadratic equation using Goal Seek | ||
Create the following table and the following named ranges: | ||
"C3" = Avalue | ||
"C4" = Bvalue | ||
"C5" = Cvalue | ||
"C7" = Xvalue |
Using Goal Seek |
Goal Seeks works by finding the closest result to the starting value (or initial guess). | ||
The problem with using Goal seek is that you have to provide an initial guess. | ||
In this example we are using the initial guess of 3. | ||
Select cell "C8" and select (Tools > Goal Seek). |
if a solution can be found to the formula then the status dialog box is displayed showing the result. |
Press OK to accept the solution and to change the cell "C7" with the solution found | ||
Pressing Cancel will return cell "C7" to its original guess of 3. |
This has only found one of the roots though so you will need to repeat the process with another guess. | ||
For our second guess we will use the value -3. |
Select cell "C7" and select (Tools > Goal Seek) |
This time the solution -2.717 has been found which must be other root. |
Using the Quadratic Formula |
It is also possible to find the solutions to a quadratic equation using the following quadratic formula: |
Checking the Results |
We can easily check these results by plotting the graph of this function. | ||
The two roots are roughly about -2.7 and 1.7 which correspond with the above results.. |
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