[m] x_{R}=\frac{x_{P}+x_{Q}}{2}=\frac{\frac{5}{3}+(-\frac{1}{2})}{2}=\frac{7}{12}[/m]
[m] y_{R}=\frac{y_{P}+y_{Q}}{2}=\frac{-1+1}{2}=0[/m]
[m] z_{R}=\frac{z_{P}+z_{Q}}{2}=\frac{\frac{1}{4}+1}{2}=\frac{1}{8}[/m]
О т в е т. R([m]\frac{7}{12};0;\frac{1}{8}[/m] )