In this tutorial, we will write a C Program to find Cosine series. Let us first by understanding what is cosine series.

**Cosine Series:**

It is a series used to find the value of cos(x), where **x** is the angle in **degree** which is converted to **Radian**.

**Formula**:

**For Cos(x) series**:

Cos(x) = 1 – (x*2 / 2!) + (x*4 / 4!) – (x*6 / 6!)……

Let us understand through a C program to calculate the value of cos(x).

**Example**

**Input**-:

x = 4, n = 3 **Output**-:

0.997563**Input**-:

x = 8, n = 2 **Output**-:

0.990266

**C Program to find Cosine series**

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | #include <stdio.h> const double PI = 3.142; int main() { float x; int n; float result = 1; float s = 1, fact = 1, p = 1; printf("Enter x value: "); scanf("%f", &x); printf("Enter n value: "); scanf("%d", &n); //Converting degrees to radians x = x *(PI / 180.0); for (int i = 1; i < n; i++) { s = s *-1; fact = fact *(2 *i - 1) *(2 *i); p = p *x * x; result = result + s *p / fact; } printf("Result: %lf\n", result); return 0; } |

**Output:**

`Enter x value: 10 `

Enter n value: 3

Result: 0.984804