\[\boxed{\mathbf{851\ (851).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\frac{a - b - a + c + b - c}{(b - c)(c - a)(a - b)} = 0\]
\[\frac{0}{(b - c)(c - a)(a - b)} = 0\]
\[0 = 0.\]