How to Find Zeros of Functions in Excel

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The zeros of a function are the values of the variable that make the function equal to zero. For example, the zeros of f(x)=x^2-1 are x=1 and x=-1. Here, the caret ^ denotes exponentiation. In Excel, you can use the Solver application to find a zero for a function using the methods of the field of mathematics called “numerical analysis.” You don’t need to know the details of the method. All you need to do is come up with a close guess as to one of the zeros of the function, and Excel will finish the job.

    Type your function into cell A1 of your Excel spreadsheet, using cell A2 in place of the variable. For example, if your function is f(x)=x^2-1, enter into cell A1 exactly the following: =A2^2-1.

    Enter your best guess in cell A2 as to what the zero of f(x) is. For example, for f(x)=x^3-3x+10, you might enter a number between -2 and -1 into cell A2, after noticing that f(-2) is -11 while f(-1) is +12. Since they are on opposite sides of zero on the number line, a zero for f(x) exists between x=-1 and x=-2.

    Go to the Tools drop-down menu at the top of the page, and select Solver. The Solver panel will pop up.

    Enter A1 into the field for “Set Target Cell.”

    Select the “Value Of” radio button, and type in the number 0, because you want Excel to make A1 equal to zero.

    Enter A2 in the field for “By Changing Cells.”

    Click the “Solve” button. The zero that Excel calculates will appear in cell A2. Solver will ask you whether you want to keep the solution. Select “OK.”

    Solve for another zero of the same function by entering another value, making sure again that it is close to where you suspect that zero is.

References

  • "Numerical Analysis;" Richard Burden and Douglas Faires; 1995

About the Author

Paul Dohrman's academic background is in physics and economics. He has professional experience as an educator, mortgage consultant, and casualty actuary. His interests include development economics, technology-based charities, and angel investing.

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