Given $a+b+c$, Can I calculate $a^2+b^2+c^2$? I want to calculate $a^2 + b^2 + c^2$  when I am given $a+b+c$.
It is known that a,b,c are positive integers.
Is there any way to find that.

If $a+b+c = k$ then $(a+b+c)^2 = k^2 \implies a^2+b^2+c^2 = k^2 - 2(ab + ac + bc)$, hence you would have to know the value of $ab + ac + bc$. 
