Quadratic Equation of the line

**Nalced4530** · 10-14-2020, 05:57 AM

Hi.

I've been asked (work) to try and get excel to generate the individual values of an equation of a line that has been plotted on the graph.

It is a quadratic 3rd order plot. y=X3+X2+X+C.

I have used the =Linest function to get the X3, X2 and X constants. I can not figure out how to get the C from the plots equation.

The reason for this, is so that x values that are found can be imported and use the pulled out values to calculate y values.

I have been told that you can put the 0 for x. I also have a foud y value for 0 but this does not give me the same values. I know they are close but that can't fly.

Is there a way to get this C value?

**MrShorty** · 10-14-2020, 08:46 AM

LINEST() should output the C parameter just like the other three parameters. You haven't explained exactly how you are using LINEST() to get the three coefficients, so I cannot say exactly what you are doing wrong that it is not giving you C as well, but LINEST() is calculating a C to with the other coefficients. It should just be a matter of seeing exactly how you are currently using LINEST() and then we should be able to figure out how to adjust to get C.

If it helps, the helpfile for LINEST() uses a cubic equation as an example (just before the main examples): https://support.microsoft.com/en-us/...rs=en-us&ad=us

**José Augusto** · 10-14-2020, 09:46 AM

Hi

Suppose your data in C3:F4 (first row - x values)

Since the data is arranged horizontally, you must use this array formula
select 1 row and four columns (ex. C6:F6), paste the formula and press Ctrl+Shift+Enter
=LINEST(C4:F4,C3:F3^ROW($A$1:$A$3))

If your data is arranged vertically (B18:C21), you must use this similar array formula
select 1 row and four columns (ex. E18:H18), paste the following formula and press Ctrl+Shift+Enter
=LINEST(C18:C21,B18:B21^COLUMN($A$1:$C$1))

See the file