К главе 3

3.1.  $\ddot{a}_D=x_1\cdot\ddot{a}_1 + x_2\cdot\ddot{a}_2 + x_3\cdot\ddot{a}_3$; $x_1=-1, x_2=1, x_3=-1$.

3.2.  $\ensuremath{\text{\textit{E}}}_D=-\ensuremath{\text{\textit{E}}}_1+\ensuremath{\text{\textit{E}}}_2$ и $$\ensuremath{\text{\textit{E}}}_D=\frac{1}{2}D_2-\frac{1}{2}D_3$$.

3.3.  $$\ensuremath{\text{\textit{Н}}}_D=\sum_{j=1}^3 x_j\cdot\ensuremath{\text{\textit{Н}}}_j$$; $x_1=-1, x_2=1, x_3=-1$.