$$a+b+c=b; a^{2}+b^{2}+c^{2}=15; (a+b)^{2}+(b+c)^{2}+(c+a)^{2}=?$$
$a=-c$
$b=d-16c^{2}$
$c\in \mathrm{R}$
$d\in \mathrm{R}$
