howto sqrt?

[Joachim Bauernberger <nuklear@singnet.com.sg>]

hi!
i'm pretty new using the gcc. most of my programming sofar has been
under windoze 8-( using the borland tools.
unfortunatly i am not able to use the sqrt or pow function. can anybody
tell me what i'm doing wrong here?

if i compile the following c program using the compiler options: gcc -g
-D_GNU_SOURCE -Wall filename.c -o outputfile
i get these errors:    undefined reference to 'sqrt'

my simple test program looks like this:

#include <stdio.h>
#include <math.h>

int main ()

{
        double  x = 900;


                       printf("\nSquare root of x = %f\n", sqrt(x));

return 0;
}

and it's the same with pow:

double x = 5, y;
y = pow(x,2);
printf("\n%g\n",y);


gives me undefined reference to pow??????

i'm sorry for boring you with newbie stuff like that.
i'd really appreaciate if anybody could help me out.....
thank's joachim!