tiny-tim, I tried to work out the problem myself out of curiosity. I know that usually, the z component is all that is asked.
I may be wrong, but it seems that the only thing to change was the denominator. I found that dB = μ0I/4∏ *(dl X r)/r^2 = μ0I/4∏ *(dl)r^2, and the x component of dB is...