[QUOTE=dhiab;332083]a,b,c is the reals numbers , Prove this equality :
Looks to me like the best thing to do is just go ahead and multiply out the right side:
Now multiply that by a+ b+ c:
[tex]c(2a^2+ 2b^2+ 2c^2- 2(ab+ac+ bc))= 2a^2c+ 2b^2c+ 2c^3- 2(abc+ ac^2+ bc^2)
Now note that the " " term in the first equation is canceled by the " " term in the second equation, etc.
Deduct all resolutions of this equation in R :