\[\boxed{\text{982.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[(a + b + c)^{2} = \left( a + (b + c) \right)^{2} =\]
\[= a^{2} + 2a(b + c) + (b + c)^{2} =\]
\[= a^{2} + 2ab + 2ac + b^{2} + 2bc +\]
\[+ c^{2} = a^{2} + b^{2} + c^{2} + 2ab +\]
\[+ 2bc + 2ac\]
\[a^{2} + b^{2} + c^{2} + 2ab + 2bc +\]
\[+ 2ac = a^{2} + b^{2} + c^{2} + 2ab +\]
\[+ 2bc + 2ac\]
\[Верно.\]