\[C - середина\ отрезка\ \text{AB.}\]
\[1)\ A(3;\ - 4),\ \ \ C(2;\ 1):\]
\[2 = \frac{3 + x}{2}\text{\ \ \ }\]
\[3 + x = 4\ \ \ \]
\[x = 1.\]
\[1 = \frac{- 4 + y}{2}\ \]
\[y - 4 = 2\ \ \]
\[y = 6.\]
\[Ответ:\ \ B(1;\ 6).\]
\[2)\ A( - 1;\ 1),\ \ \ C(0,5;\ - 1):\]
\[0,5 = \frac{- 1 + x}{2}\text{\ \ \ }\]
\[x - 1 = 1\ \ \ \]
\[x = 2.\]
\[- 1 = \frac{1 + y}{2}\ \]
\[1 + y = - 2\ \]
\[y = - 3.\]
\[Ответ:\ \ B(2;\ - 3).\]