# Recipe 2.11 Calculating More Trigonometric Functions

#### 2.11.1 Problem

You want to calculate values for trigonometric functions like sine, tangent, or arc-cosine.

#### 2.11.2 Solution

Perl provides only sin, cos, and atan2 as standard functions. From these, you can derive tan and all other trig functions (if you're intimately familiar with esoteric trig identities):

```sub tan {
my \$theta = shift;

return sin(\$theta)/cos(\$theta);
}```

The POSIX module provides a wider range of trig functions:

```use POSIX;

\$y = acos(3.7);```

The standard Math::Trig module provides a complete set of functions and supports operations on or resulting in complex numbers:

```use Math::Trig;

\$y = acos(3.7);```

#### 2.11.3 Discussion

The tan function will cause a division-by-zero exception when \$theta is p/2, 3p/2, and so on, because the cosine is 0 for these values. Similarly, tan and many other functions from Math::Trig may generate the same error. To trap these, use eval:

```eval {
\$y = tan(\$pi/2);
} or return undef;```

The sin, cos, and atan2 functions in perlfunc(1) and Chapter 29 of Programming Perl; the documentation for the standard Math::Trig module; we talk about trigonometry in the context of imaginary numbers in Recipe 2.14; we talk about the use of eval to catch exceptions in Recipe 10.12

 Chapter 1. Strings
 Chapter 3. Dates and Times
 Chapter 4. Arrays
 Chapter 5. Hashes
 Chapter 6. Pattern Matching
 Chapter 7. File Access
 Chapter 8. File Contents
 Chapter 9. Directories
 Chapter 10. Subroutines
 Chapter 11. References and Records
 Chapter 12. Packages, Libraries, and Modules
 Chapter 13. Classes, Objects, and Ties
 Chapter 14. Database Access
 Chapter 15. Interactivity
 Chapter 16. Process Management and Communication
 Chapter 17. Sockets
 Chapter 18. Internet Services
 Chapter 19. CGI Programming
 Chapter 20. Web Automation
 Chapter 21. mod_perl
 Chapter 22. XML