how the coulomb's law formula is given, and why the formula is given in that way and not in other way

@ xavier 
when coulomb tested with two charges as expertimental material , then he found that , the force of attraction between these two charges , will be directly proportional to the magnitude of two charge and inversely prop to the radius or distance between them . 
when he increase the distance then force decreases . 

for that reason he gave and formulated his first law as coulombs law . 
and other scientist also came with the same conclusion , so ,nonne can oppose or argue with his law . 
THERE IS NO SUCH PROOF FOR IT . 
HOPE IT CLEARS NOW 
ALL THE BEST ..