Inside Macintosh: Operating System Utilities /
Chapter 3 - Mathematical and Logical Utilities / Mathematical and Logical Utilities Reference
Routines / Performing Calculations on Fixed-Point Numbers

### FixATan2

You can use the `FixATan2` function to obtain a fast approximation of the arctangent of a fraction.

```FUNCTION FixATan2 (x, y: LongInt): Fixed;
```
`x`
The numerator of the fraction whose arctangent is to be obtained. This variable can be a `LongInt`, `Fixed`, or `Fract` number.
`y`
The denominator of the fraction whose arctangent is to be obtained. The number supplied in this variable must be of the same type as that of the number supplied in the `x` parameter.
##### DESCRIPTION
The `FixATan2` function returns, in radians, the arctangent of `y/x`.

The approximation of Pi/4 used to compute the arctangent is the hexadecimal value 0.C910, making the approximation of Pi equal to 3.1416015625, while Pi itself equals 3.14159265.... Thus `FixATan2(1, 1)`equals the equivalent of the hexadecimal value 0.C910. Despite the approximation of Pi, the arctangent value obtained will usually be correct to several decimal places.