# Special Functions

Excel has a very large number of special functions that you can use in a cell
formula. We list only a few here. You can see a
complete listing in Excel by going to the Insert menu and choosing "Function."
A dialog box will appear giving lists of functions you can paste into a cell,
with some documentation for each.

## Exponential and Logarithmic Functions

Excel has an exponential function and a natural log function. =EXP(*value*)
gives the result of *e*^{value}. For example, to find the value
of *e*^{2 x-1}, where *x* is to be taken from cell A2,
you would use the formula =EXP(2*A2-1). (In other
words, whatever is in the exponent goes in the parentheses.)

The natural log is LN, and works the same way. So
ln(A2) would be written as =LN(A2). (Careful with
this one! Excel has another function called LOG which
is a *different* kind of logarithm. Don't use LOG
for the natural log!)

## Sums

You can add everything in a region by using the SUM command. For example, to
add up all the entries in the cells starting at A2 and ending at A23, you would
enter the command =SUM(A2:A23). (This uses a range
cell reference; see Cell References.)

*Hint on entering the range:* Excel has a nice shortcut for entering
cell ranges. Start your formula as usual with "=SUM("
and then simply click on the first cell you want to include in your range and
drag to the last cell you want to include. Excel will highlight these cells
and fill in the correct range. Then just finish with the closing parenthesis.

## Pi

The number pi is represented in Excel as a function with no arguments; thus
=PI() returns approximately 3.14159.

## Square Roots

Excel has a square root function SQRT(). Thus, =SQRT(25)
returns 5. Of course, you can also raise a number to the 1/2 power; so =(25)^0.5
also returns 5.

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