error w/out -lm flag

gcc first.c -o first
/usr/bin/ld: /tmp/cctTS68G.o: in function `main':
first.c:(.text+0x2e): undefined reference to `sqrt'
/usr/bin/ld: first.c:(.text+0x8c): undefined reference to `pow'
collect2: error: ld returned 1 exit status