math problems

[jmeisenh]

I have recently discovered a problem while attempting to write a program in C.
Whenever i attempt to use any of the math functions, for example, pow(), sqrt(),
sin(), cos(), the compiler says it is an undefined reference to whichever math
function i am using. 
Odly enough, i have found a way to use the pow() and sqrt() function by adding
the -O option when i compile ( i do not understand why that works, but it does)
however I still cannot get the trigonometric identities to work, even though i
include math.h in my program. 
please get back to me and tell me what can be done about this problem. Thank you