# NumPy cos()

The `cos()` function computes the cosine of the elements in an array.

The cosine is the trigonometric function that calculates the ratio of the length of the side adjacent to an angle to the length of the hypotenuse in a right-angled triangle.

### Example

``````import numpy as np

# array of angles in radians
angles = np.array([0, 1, 5])

# compute the cosine of the angles
cosineValues = np.cos(angles)

print(cosineValues)

# Output : [1.         0.54030231 0.28366219]``````

## cos() Syntax

The syntax of `cos()` is:

``numpy.cos(array, out = None, dtype = None)``

## cos() Arguments

The `cos()` function takes following arguments:

• `array` - the input arrays
• `out` (optional) - the output array where the result will be stored
• `dtype` (optional) - data type of the output array

## cos() Return Value

The `cos()` function returns an array containing the element-wise cosine values of the input array.

## Example 1: Compute cosine of the Angles

``````import numpy as np

# array of angles in radians
angles = np.array([0, np.pi/4, np.pi/2, np.pi])
print("Angles:", angles)

# compute the cosine of the angles
cosineValues = np.cos(angles)

print("cosine values:", cosineValues)``````

Output

```Angles: [0.         0.78539816 1.57079633 3.14159265]
cosine values: [ 1.00000000e+00  7.07106781e-01  6.12323400e-17 -1.00000000e+00]```

In this example, we have the array angles containing four angles in radians: 0, π/4, π/2, and π.

The `np.cos()` function is used to calculate the cosine values for each element in the angles array.

## Example 2: Use out to Store the Result in Desired Location

``````import numpy as np

# create an array of angles in radians
angles = np.array([0, np.pi/6, np.pi/4, np.pi/3, np.pi/2])

# create an empty array to store the result
result = np.empty_like(angles)

# compute the cosine of angles and store the result in the 'result' array
np.cos(angles, out=result)

print("Result:", result)``````

Output

```Result: [1.00000000e+00 8.66025404e-01 7.07106781e-01 5.00000000e-01
6.12323400e-17]```

Here, we have used `cos()` with the `out` parameter to compute the cosine of the angles array and store the result directly in the result array.

The resulting result array contains the computed cosine values.

## Example 3: Use of dtype Argument in cos()

``````import numpy as np

# create an array of angles in radians
angles = np.array([0, np.pi/4, np.pi/2, np.pi])

# calculate the cosine of each angle with a specific dtype
floatCosines = np.cos(angles, dtype=float)
complexCosines = np.cos(angles, dtype=complex)

print("Cosines with 'float' dtype:")
print(floatCosines)

print("\nCosines with 'complex' dtype:")
print(complexCosines)``````

Output

```Cosines with 'float' dtype:
[ 1.00000000e+00  7.07106781e-01  6.12323400e-17 -1.00000000e+00]

Cosines with 'complex' dtype:
[ 1.00000000e+00-0.j  7.07106781e-01-0.j  6.12323400e-17-0.j
-1.00000000e+00-0.j]```

Here, by specifying the desired `dtype`, we can control the data type of the output array according to our specific requirements.

Note: To learn more about the `dtype` argument, please visit NumPy Data Types.