To find the cosine of a number (in radians), we can use the php **cos()** function.

`cos(x)`

In php, we can easily use trigonometric functions from the collection of php math functions. These php math functions allow us to perform trigonometry easily.

To find the cosine of a number, in radians, we use the php **cos()** function.

Below is the php syntax to find the cosine of a number.

`cos(x)`

The input to the **cos()** function must be a float. The return value will be a float between -1 and 1.

```
echo cos(pi()/3); // 0.5000000000000001
echo cos(0); // 1.0
echo cos(pi()/2); // 6.123233995736766e-17
```

## Converting Degrees to Radians for Input into cos()

The **cos()** function takes a number in radians as input. If your data is in degrees, you will need to convert the values to radians.

To convert degrees to radians, we can use the php deg2rad() function to convert the value to radians and then pass it to the **cos()** function.

```
echo cos(deg2rad(60)); // 0.5000000000000001
echo cos(deg2rad(0)); // 1.0
echo cos(deg2rad(90)); // 6.123233995736766e-17
```

## Finding the Inverse Cosine of a Number in php

With php, we can also find the inverses of the common trigonometric functions. The acos() function allows us to find the inverse of the cosine of a number.

Below, we show that if we pass a number to **sin()** and then call the php **asin()** function, we get back the same number.

```
echo asin(cos(pi()/3)); // 1.0471975511965976
echo pi()/3; // 1.0471975511965976
```

## Finding the Secant of a Number in php

To find the secant of a number, we can divide 1 by the cosine of the number.

We can find thesecant of a number easily with the php **cos()** function. You can see how to find the cosecant of a number in the following php code.

`echo 1/cos(pi()/3); // 1.9999999999999996`

Hopefully this article has been beneficial for you to understand how to use the **cos()** function in php to find the cosine of a number.

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