How to Solve a Cubic Equation in Excel (2 Ways)

We’ve arranged the equation on a worksheet using the following image for our calculation process. Here, we have shown the variables and the coefficients separately.

2 Easy Ways to Solve Cubic Equation in Excel

Method 1 – Utilizing the Goal Seek Feature to Solve a Cubic Equation in Excel

Steps:

Make a new table under the main data set to show the results after calculation.
Set 0 as the initial value of X.

Utilizing Goal Seek Feature to Solve Cubic Equation in Excel

Use the following formula to determine the value of Y when the initial value of X is zero.

=B13^3*C5+B13^2*C6+B13*C7+C9

Press Enter to get the value for Y, which is 12.

After finishing all the calculations, go to the Forecast group of the ribbon.
Choose the What-If Analysis.

From the dropdown menu, select Goal Seek.

We will solve an equation for X when Y is given.
After choosing the command from the previous step, you will see the Goal Seek dialog box.
In the “Set cell” type box, input the cell address that will be the final output of this goal.
In the “To value” type box, set the new output for the cell chosen in the previous step.
In the “By changing cell” type box, select the cell, and we will get the above outcome by altering it.
Press OK.

After pressing OK, the Goal Seek feature will take some time to show the result after calculation.
Here, to change the value of Y to 20, the value of X must be around 0.36304, which is one of the roots of this cubic equation.

Method 2 – Using Solver Add-in to Solve a Cubic Equation

Steps:

Make a data table to show the results, just like the previous method.
Calculate the value of Y from the formula shown in the previous discussion.

Before going to the calculator, we need to activate the add-in.
Go to the File tab of the ribbon.

Select Options from the Excel Home window.

Go to the Add-ins tab in the Excel Options dialog box.
In the Manage section, choose Excel Add-ins and select Go.

Mark the box beside Solver Add-in and press OK.

You will see the Solver command in the Data group.
Click on it.

You will see the Solver Parameters dialog box.
We have to set some parameters.
In the Set Objective type box, select cell C13, which has a value of Y.
Set the “Value Of” type box to 20. This sets the value of Y.
Get the output 20 by changing the X value in cell B13.
Ensure the solving method is nonlinear, as our equation is not linear.
Press Solve.

After reviewing all the inputs, the Solver will show the final result.
In our case, the value of X is 0.36304.
If we enter this value into the equation, we will get the value of Y as 20.

Notes

As both the Goal Seek and Solver need to input a value first for the calculation, you have set the value of Y = 20 in the first place.
As in many cases, a cubic equation may have a simple root and more than one complex root. So, both the above methods will show the simple root.

Download the Practice Workbook

You can download the free Excel workbook here to practice.

Solving Cubic Equation.xlsx