一道作业题： 指数函数出错请问 pow(num, 0.25)

一道作业题： 指数函数出错请教 pow(num, 0.25)
#include   <stdio.h>
#include   <math.h>
int   main()
{
    float   num,   result;

    printf( "Enter   a   number   here:   ");
    scanf( "%f ",   &num);
    result   =   pow(num,   0.25);
    printf( "%f   raised   to   the   1/4   thd   power   is   %f\n ",   num,   result);

    return   0;
}

编译时提示
$   gcc   -o   3_6_5   3_6_5.c
/tmp/ccIOqWWD.o:   In   function   `main ':
3_6_5.c:(.text+0x47):   undefined   reference   to   `pow '
collect2:   ld   返回   1


请教一下时怎么回事

[解决办法]
改成这样

result = pow(num, 0.25f);


[解决办法]
result = (float)pow((double)num, 0.25);
[解决办法]
#include <stdio.h>
#include <math.h>
int main()
{
float num, result;-----double num,result;

printf( "Enter a number here: ");
scanf( "%f ", &num);----------------- "%f "---> "%lf "
result = pow(num, 0.25);
printf( "%f raised to the 1/4 thd power is %f\n ", num, result);

return 0;
}