How PHP’s sin() Function Handles Negative Inputs and Their Effects on Results

gitbox 2025-09-03

In PHP, the sin() function is used to calculate the sine of an angle, and its syntax is straightforward:

<span><span><span class="hljs-keyword">float</span></span><span> </span><span><span class="hljs-title function_ invoke__">sin</span></span><span>(</span><span><span class="hljs-keyword">float</span></span><span> </span><span><span class="hljs-variable">$arg</span></span><span>)
</span></span>

Here, $arg is the angle in radians. It’s important to note that PHP’s sin() function requires the parameter to be in radians, not degrees. If you have a degree value, you need to convert it first using deg2rad().

Handling Negative Inputs

When a negative value is passed to the sin() function, PHP directly calculates the sine of that negative radian. Mathematically, the sine function is odd, meaning:

<span><span><span class="hljs-built_in">sin</span></span><span>(-x) = -</span><span><span class="hljs-built_in">sin</span></span><span>(x)
</span></span>

This means that if you pass a negative value to sin(), the return value is simply the negative of the sine of the corresponding positive value.

Example

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$positive</span></span><span> = </span><span><span class="hljs-title function_ invoke__">pi</span></span><span>() / </span><span><span class="hljs-number">4</span></span>;   </span><span><span class="hljs-comment">// π/4 radians</span></span><span>
</span><span><span class="hljs-variable">$negative</span></span><span> = -</span><span><span class="hljs-title function_ invoke__">pi</span></span><span>() / </span><span><span class="hljs-number">4</span></span>;  </span><span><span class="hljs-comment">// -π/4 radians</span></span><span>
<p></span>echo "sin(π/4) = " . sin($positive) . "\n"; // approximately 0.7071<br>
echo "sin(-π/4) = " . sin($negative) . "\n"; // approximately -0.7071<br>
?><br>
</span>

As shown, negative radian inputs do not cause errors; PHP returns the correct negative value according to mathematical principles.

Effects of Negative Values on Results

Sign Change
- The sine output follows the input’s sign: positive radians return positive values, negative radians return negative values.
Amplitude Remains the Same
- The absolute value of sine does not exceed 1, regardless of whether the input is positive or negative.
Periodicity Unaffected
- The sine function is periodic, with a period of $2\pi$ , so negative radians only reverse the angle direction but do not affect the overall periodic nature of the function.

Summary

When using PHP’s sin() function with negative inputs:

PHP calculates it directly according to the rules for odd functions.
The output sine value is the negative of the corresponding positive radian.
The function’s range and periodic properties remain unaffected.

Therefore, developers can confidently use negative numbers as parameters for sin() without worrying about unexpected results.

sin
deg2rad