x_(C)=(-3+([red]4/1[/red])*7)/(1+([red]4/1[/red]))=(25/5)=[b]5[/b]
y_(C)=(-4+([red]4/1[/red])*1)/(1+([red]4/1[/red]))=(0/5)=[b]0[/b]
z_(C)=(6+([red]4/1[/red])*(-9))/(1+([red]4/1[/red]))=(-30)/5=[b](-6)[/b]
[m]ОС=\sqrt{5^2+0^2+(-6)^2}=\sqrt{61}[/m] - о т в е т