 ### Program 171:To Print value of Cosine Mathematically and using Library Function

Program 171:

```#include<stdio.h>
#include<math.h>
int factorial(int);
main()
{
//cos x = 1 - x 2 / 2! + x 4 / 4! - x 6 / 6! + ...
int accuracy,count=0,k=0;
float x,temp,cosine=0;

printf("Enter value x(in degrees) to find cos x value\n");
scanf("%f",&x);
temp=x;
x=(float)x*(3.14159/180);
printf("Enter value to get more accurate\n 3 for least and more for more accuracy\n");
scanf("%d",&accuracy);

do
{
if(count%2==0)
{
cosine=(float)cosine+(pow(x,k)/factorial(k));
}
if(count%2==1)
{
cosine=(float)cosine-(pow(x,k)/factorial(k));
}
count++;
k=k+2;
}while(count<=accuracy);

printf("cos(%f)=%f calcualted mathematically\n",temp,cosine);
printf("cos(%f)=%f calculated using library function\n",temp,cos(x));
}

int factorial(int val)
{
int factorial=1,i;
for(i=1;i<=val;i++)
{
factorial=factorial*i;
}
return(factorial);

}

```
Explanation:

The Explanation is same as the program 170 to print sine value except the formula is changed to
`cos x = 1 - x 2 / 2! + x 4 / 4! - x 6 / 6! + ...`
`Here k is initialized to 0 for getting even number powers to base etc `

Output: 