[m] x_{O}=\frac{x_{A}+x_{C}}{2}=\frac{-4+4}{2}=0[/m]
[m] y_{O}=\frac{y_{A}+y_{C}}{2}=\frac{-8+0}{2}=-4[/m]
[m] z_{O}=\frac{z_{A}+z_{C}}{2}=\frac{8+(-10)}{2}=-1[/m]
O- середина BD
[m] x_{O}=\frac{x_{B}+x_{D}}{2}[/m] ⇒ [m]x_{D}=2x_{O}-x_{B}=2\cdot 0-(-2)=2[/m]
[m] y_{O}=\frac{y_{B}+y_{D}}{2}[/m] ⇒ [m]y_{D}=2y_{O}-y_{B}=2\cdot (-4)-(-2)=-6[/m]
[m] z_{O}=\frac{z_{B}+z_{D}}{2}[/m] ⇒ [m]z_{D}=2z_{O}-z_{B}=2\cdot (-1)-6=-8[/m]