Arithmetic and Geometric Series

Arithmetic Series

This is the easiest way to get the series 2, 4, 6, 8, 10, 12. The formula, =A1+2, in cell A2, simply adds 2 to the previous cell. Once you create the formula in cell A2, you can highlight cells A2 through A6 and use Fill Down from the Calculate menu to copy the formula to the rest of the cells. To highlight cells A2 through A6, click on cell A2, then while holding down the mouse button, drag to cell A6 and release the mouse button.

This is another way to get the same series. Enter the increment value, 2, into cell A2, and the formula, =B1+A$2 into cell B2. Then use Fill Down again.

It's a little more difficult to set up but once you do, you can change the increment value in cell A2 and the computer will automatically create a new series with that increment. For example, with a value of 2 in cell A2, you get the series 2, 4, 6, 8, 10, 12. If you change the value in cell A2 to 3, you get the series 2, 5, 8, 11, 14, 17.

How could you get the series 3, 6, 9, 12, 15, 18?

Notice the $ in the formulas in cells B2 through B6. The dollar sign, $, in the cell reference, A$2, tells the computer to not change the row number when you use the Fill Down command. This is called absolute addressing.

The graph of an arithmetic series is a straight line.

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Geometric Series

The formula, =A1*2 in cell A2 multiplies the previous cell by 2. Again, use fill down to copy this formula into cells A3 through A6. This will produce the series 2, 4, 8, 16, 32, 64.

We used absolute addressing for the arithmetic series problem to make it easier to change the increment value. Can you figure out how to use absolute addressing for the geometric series problem?

The graph of a geometric series is a rapidly growing curve (exponential growth).

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