14.3: I'm trying to do some simple trig, and I am #including <math.h>, but I keep getting "undefined: sin" compilation errors.
A: Make sure you're actually linking with the math library. For instance, due to a longstanding bug in Unix and Linux systems, you usually need to use an explicit -lm flag, at the end of the command line, when compiling/linking. See also questions 13.25, 13.26, and 14.2.
gcc -o triangle triangle.c -lm