That's a big approximation, mbonwick.
I've finished with maths, but I have done an Advanced Higher (eqv. A Level) so if I can be of any assistance, please feel free to PM me!
There's not really much more to pi than has been said above. pi.rad=180deg, approximately equal to 3.142.
With regards to radians, I don't know if you're doing calculus, but remember that radians is always used in calculus, never degrees. To convert from degrees to radians, multiply the number of degrees by pi/180. Similarly to convert back to degrees, multiply number of radians by 180/pi. If you're bot doing radians, ignore that last paragraph.