# \$ZARCCOS

Inverse (arc) cosine function.

## Synopsis

```\$ZARCCOS(n)
```

### Parameter

Argument Description
n A signed decimal number.

## Description

\$ZARCCOS returns the trigonometric inverse (arc) cosine of n. The result is given in radians (to 18 decimal places).

## Parameter

### n

Signed decimal number ranging from 1 to -1 (inclusive). It can be specified as a value, a variable, or an expression. Numbers outside the range generate an <ILLEGAL VALUE> error. A non-numeric string is evaluated as 0.

The following are arc cosine values returned by \$ZARCCOS:

 1 returns 0 0 returns 1.570796326794896619 -1 returns pi (3.141592653589793238)

## Examples

The following example permits you to compare the arc cosine and the arc sine of a number:

``````   READ "Input a number: ",num
IF num>1 { WRITE !,"ILLEGAL VALUE: number too big" }
ELSEIF num<-1 { WRITE !,"ILLEGAL VALUE: number too small" }
ELSE {
WRITE !,"the arc cosine is: ",\$ZARCCOS(num)
WRITE !,"the arc sine is: ",\$ZARCSIN(num)
}
QUIT``````

The following example compares the results from Caché fractional numbers (\$DECIMAL numbers) and \$DOUBLE numbers. In both cases, the arc cosine of 1 is exactly 0:

``````  WRITE !,"the arc cosine is: ",\$ZARCCOS(0.0)
WRITE !,"the arc cosine is: ",\$ZARCCOS(\$DOUBLE(0.0))
WRITE !,"the arc cosine is: ",\$ZARCCOS(1.0)
WRITE !,"the arc cosine is: ",\$ZARCCOS(\$DOUBLE(1.0))
WRITE !,"the arc cosine is: ",\$ZARCCOS(-1.0)
WRITE !,"the arc cosine is: ",\$ZARCCOS(\$DOUBLE(-1.0))``````