DISCOVER

# How to Use Excel to Solve a Polynomial

Updated February 21, 2017

A polynomial in mathematics is the sum of a number of terms that are added, subtracted, or multiplied. A polynomial can have one term like 1, x, y, or z, or it can have multiples terms: for example, x^3 + 10 ^ 2 + 4 is a polynomial. Solving a polynomial means that you have to find a value for the X in the equation. This is sometimes called finding a root of a polynomial or finding the zeros. Excel can do this task for you.

Input the coefficients into separate cells in row 4 in Excel, starting at cell "B4." for example, if you have a cubic equation x^3 - 2x^2 - 3x, then your coefficients are 1, -2, 6 and -3. Click on cell "B4" and type "1", then click on cell "C4" and type "-2," then click on cell "D4" and type "6," then click on cell "E4" and type "-3."

Click on cell "B6" and type a guess for the value of X. If you have no idea of what the value might be, just type "0."

Click on cell "G4" and then type the full equation into the cell. In this example, the equation would be "x^3 - 2x^2 - 3x."

Click on the "Data" tab, then click on "What-If Analysis," in the Data Tools group and then click "Goal Seek."

Click on the "Set cell" text box and type "G4."

Click on the "To value" text box and then type "0."

Click on the "By changing cell" text box and then type "\$B\$6."

Click on "OK." Excel will solve the polynomial and return the result in cell B6 (the initial guess box).

#### Tip

Make sure that the polynomial you enter is actually a polynomial. If your equation has any division in it, or if your exponents are negative, the equation is not a polynomial and therefore the Excel Goal Seek function will either return an error or it may return a wrong answer.

#### Things You'll Need

• Excel 2007 or Excel 2010