Stephanie  -

You should use your judgment to decide whether the linear trend or the
quadratic trend is appropriate.

The quadratic trend uses ^{1,2} to obtain both x and x^2 values as
explanatory variables so that the fitted values have some curvature, i.e.,
polynomial of order 2, also called a quadratic.

The TREND function must be array-entered (and a formula that uses ^{1,2}must
be array-entered). To array-enter the function, select the range of cells
that will contain the function results, type the =TREND(...) function with
appropriate arguments but do not press Enter, instead after typing the
closing parentheses hold down Control and Shift keys while you press Enter,
thus "array-entering" the function.

-  Mike

^{1,2} assumes that the data are in columns.  Use ^{1;2} if the data are in
rows.

Jerry