How to Solve a Quadratic Equation Using the Goal Seek Feature on Microsoft Excel

Step-by-Step Guide

1. 1

   Step 1: Launch the Microsoft Excel 2010 program.

   This procedure can be applied to Microsoft Excel 2013 or earlier versions of Microsoft Excel as long as it has the Goal Seek feature.
2. 2

   Step 2: Locate the equation you plan on solving and re-arrange the equation to equal zero.

   For this example, we will use a quadratic equation of the form ax^2+bx+c=0.
   
   To do this, we will need to rearrange the equation so that the right hand side is equal to zero. , For a quadratic with an order of 2, the expected possibilities are two roots or no roots. , You can do this by simply picking the cells you want to use.
   
   For this example, we will use four cells in total.
   
   We have arbitrarily chosen the block between A1 and B2. , “X-Value” will be a guess for the root, or solution, to the equation. “Equ=0” will be your equation set equal to zero. , Put in a guess for the solution to the quadratic equation.
   
   Remember, we do not know the solution so we must guess! Since we are looking for the higher (or more positive root), it is best to guess a double digit positive number.We will choose positive 10 as a guess.Press Enter. , Enter by putting “=” and put equation in by selecting X-value (A2 Cell) guess as variable.
   
   Press Enter. ,,,, This was the purpose of re-arranging our equation to equal to zero. , Excel will compute the solution by changing this guess until the input equation is equal to zero. , The “Goal Seek Status” window will appear.
   
   As you can see, Equ=0 converges to a small value that is close to zero, while the solution can be found under the “X-Value” header as
   3. , This time, we will choose negative 10 to capture the lower root in Excel's solution process. , Equ =0 should converge to a small value that is close to zero, while the solution can be found under the “X-Value” header as
   -1. ,
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   Step 3: Figure out your expected number of roots (solutions).

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   Step 4: Select cells to work with.

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   Step 5: Label a cell “X-value” and an adjacent cell in the same row “Equ=0”.

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   Step 6: In the row below “X-Value” in the same column

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   Step 7: put in a guess value for x.

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   Step 8: In the row below “Equ=0” in the same column

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   Step 9: put in your re-arranged equation using the X-value guess in step 3 as your variable.

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    Step 10: Find and click the “Data” tab on the top of the Excel spreadsheet.

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    Step 11: Click “What-if Analysis” and select “Goal Seek” from the drop down tab.

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    Step 12: Click the cell used to input your equation in Part 2

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    Step 13: Step 4 under the "Set Value" field.

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    Step 14: Type in zero under the "To value" field (see figure above).

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    Step 15: Click the cell used to input your guess x-value under the “By changing cell” field(see figure above).

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    Step 16: Press “Ok” to solve.

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    Step 17: Find the lower root by entering another guess for the X-Value.

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    Step 18: Repeat all steps in part 3 for the different guess.

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    Step 19: Prove your answers though graphical methods or algebraic (factoring methods).

Detailed Guide

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