c语言 求对数问题,#include"stdio.h"#include"math.h"void main(){double a,b;a=2*3.14-1;b=log5(sqrt(a));printf("%f\n");getchar();}error C2065: 'log5' : undeclared identifier 应怎样改啊?谢谢

c语言 求对数问题,#include"stdio.h"#include"math.h"void main(){double a,b;a=2*3.14-1;b=log5(sqrt(a));printf("%f\n");getchar();}error C2065: 'log5' : undeclared identifier 应怎样改啊?谢谢
c语言 求对数问题,
#include"stdio.h"
#include"math.h"
void main()
{
double a,b;
a=2*3.14-1;
b=log5(sqrt(a));
printf("%f\n");
getchar();
}error C2065: 'log5' : undeclared identifier 应怎样改啊?谢谢

c语言 求对数问题,#include"stdio.h"#include"math.h"void main(){double a,b;a=2*3.14-1;b=log5(sqrt(a));printf("%f\n");getchar();}error C2065: 'log5' : undeclared identifier 应怎样改啊?谢谢
C语言中没有以任意为底数的对数函数,所以log5是没有的.所以可以用logx(y)=log(y)/log(x)来代替,修改代码如下
#include"stdio.h"
#include"math.h"
void main()
{
\x09double a,b;
\x09a=2*3.14-1;
\x09b=log(sqrt(a))/log(5);
\x09printf("%f\n",b);
\x09getchar();
}