# PHP Math - asin() Function

The PHP Math asin() function returns arc sine of a value. The return value will be in the range -𝜋/2 through 𝜋/2. In special cases it returns the following:

• If the argument is NAN or its absolute value is greater than 1, then the result is NAN.

Note: asin() is the inverse of sin().

### Syntax

```asin(number)
```

### Parameters

 `number` `Required. `Specify the value.

### Return Value

Returns the arc sine of the value.

### Example:

In the example below, asin() function is used to find out the arc sine of a given value.

```<?php
echo "asin(-1) = ".asin(-1)."\n";
echo "asin(-0.5) = ".asin(-0.5)."\n";
echo "asin(0) = ".asin(0)."\n";
echo "asin(0.5) = ".asin(0.5)."\n";
echo "asin(1) = ".asin(1)."\n";
echo "asin(2) = ".asin(2)."\n";
echo "asin(NAN) = ".asin(NAN)."\n";
?>
```

The output of the above code will be:

```asin(-1) = -1.5707963267949
asin(-0.5) = -0.5235987755983
asin(0) = 0
asin(0.5) = 0.5235987755983
asin(1) = 1.5707963267949
asin(2) = NAN
asin(NAN) = NAN
```

❮ PHP Math Functions

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