Daniel,
you can use the built-in help in Numbers while entering formulas:
to access the built-in help,
- select the cell where you want to enter the formula
- open the formatter (top right):
- enter the function you want in the cell, or search for the function in the built-in help to see the details for each function.
from the built-in help, here is the description for FORECAST:
The FORECAST function returns the forecasted y value for a given x based on sample values using linear regression analysis.
FORECAST(x-value, y-values, x-values)
x-value: The x value for which the function should return a forecasted y value. x-value must contain a number value, date/time value, or duration value.
y-values: The collection containing the y (dependent) values. y-values must contain number values, date/time values, or duration values. All values must be of the same value type.
x-values: The collection containing the x (independent) values. x-values must contain number values, date/time values, or duration values. All values must be of the same value type.
so you need X and Y values, you have only provided (I am guessing) Y values.
assuming that the Y values are equally spaced in X, I am going to make up some X data. made up X values in column B, and your Y values in column C. For forecast value in column D:
D22=FORECAST(B22,C2:C21,B2:B21)
this is shorthand for... select cell D22, then type (or copy and paste from here) the formula:
=FORECAST(B22,C2:C21,B2:B21)
