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# \$ZARCSIN

Inverse (arc) sine function.

## Synopsis

```\$ZARCSIN(n)
```

### Parameter

Argument Description
n A signed decimal number.

## Description

\$ZARCSIN returns the trigonometric inverse (arc) sine of n. The result is given in radians.

## 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 sine values returned by \$ZARCSIN:

 1 returns 1.570796326794896619 0 returns 0 -1 returns -1.570796326794896619

## Examples

The following example permits you to compare the arc sine and the arc cosine 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 sine is: ",\$ZARCSIN(num)
WRITE !,"the arc cosine is: ",\$ZARCCOS(num)
}
QUIT```

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

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

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