Hold on, I don't concur, and you don't deserve all those thanks. Your geosynchronous orbit value is off by 6x10^3 Km. I have provided the calc below for proof:
Centripetal Force of satellite=mrw^2
Force on satellite acting from earth's center=GMm/r^2
Since the Force 2 is acting perpendicular along a tangent line of the circular orbit, we can say force no. 2 IS the satellite's centripetal force.
Hence, F1=F2.
Hence, GMm/r^2=mrw^2
In this sense, the mass of the satellite cancels out.
w=angular velocity, in radians sec^-1. Since there are 86,400 secs in a day, there are 2π/86,400 radians in a sec, canceling gives us π/43,200.
Now, GM/r^2=r(π/43,200)^2
Hence, 43,200^2GM/π^2=r^3
Solving for r, that is distance from center of earth to the satellite, it gives us ~42x10^3 KM. Since you're speaking of orbits, it's always given from a point source, that is, the whole mass of something is taken at a single point, the center of earth in this case.