Даны точки М(0;1;1),N(2;-1;3),K(-1;y;0). Найдите такое значение у,чтобы выполнялось условие МК=NK
[m]=\sqrt{(-1-0)^2+(y-1)^2+(0-1)^2}=\sqrt{2+(y-1)^2}[/m]
[m]NK=\sqrt{(x_{K}-x_{N})^2+(y_{K}-y_{N})^2+(z_{K}-z_{N})^2}=[/m]
[m]=\sqrt{(-1-2)^2+(y-(-1))^2+(0-3)^2}=\sqrt{18+(y+1)^2}[/m]
[m] MK=NK[/m]
[m]\sqrt{2+(y-1)^2}=\sqrt{18+(y+1)^2}[/m]
Возводим в квадрат:
[m]2+(y-1)^2=18+(y+1)^2[/m]
[m](y-1)^2-(y+1)^2=18-2[/m]
[m](y-1-(y+1))\cdot (y-1+y+1)=16[/m]
[m](-2)\cdot (2y)=16[/m]
[m]-4y=16[/m]
[m]y=-4[/m] - о т в е т