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#  Chapter 2Numbers ## 2.12. Calculating More Trigonometric Functions

### Problem

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

### Solution

Perl provides only `sin`, `cos`, and `atan2` as standard functions. From these, you can derive `tan` and the other trig functions:

```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 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);```

### Discussion

The `tan` function will cause a division-by-zero exception when `\$theta` is , , 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 3 of Programming Perl; we talk about trigonometry in the context of imaginary numbers in Recipe 2.15; we talk about the use of `eval` to catch exceptions in Recipe 10.12   2.11. Doing Trigonometry in Degrees, not Radians 2.13. Taking Logarithms