Why do you have to link the math library in C?

Question

If I include or in a C program I don\'t have to link these when compiling but I do have to link to

Answer 1

Because time() and some other functions are builtin defined in the C library (libc) itself and GCC always links to libc unless you use the -ffreestanding compile option. However math functions live in libm which is not implicitly linked by gcc.