用C语言求cosX的值

x -- 用弧度值输入
精度 -- 1E-07
泰勒公式:
cos(x) = 1 - x^2/2! + x^4/4! - x^6/6! ...
程序：
#include<stdio.h>
#include<math.h>
void main(){
double x,term,sum,x2;
int i;

printf("input x in HuDu\n");
scanf("%lf",&x);
x2 = x * x;
sum = 1.0;
term = 1.0;

for (i=2;i<20;i=i+2){
term = term*x2/(double) (i * (i-1)) * (-1.0);
if (fabs(term) < 1.0E-07) break;
sum = sum + term;
}
printf("cos(x)=%lf\n",sum);
}

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算例：
1.570796
cos(x)=0.000000
0.78539
cos(x)=0.707113
3.14159
cos(x)=-1.000000