To prove: Points A, B, C form equilateral triangle.
Formula: The distance between two points (x1,y1,z1) and (x2,y2,z2) is given by
D = \(\sqrt{(x_2-x_1)^2+(y_2-y_1)^2+(z_2-z_1)^2}\)
Here,
(x1,y1,z1)= (1, -1, -5)
(x2,y2,z2)= (3, 1,3)
(x3,y3,z3)= (9, 1, -3)
Length AB = \(\sqrt{(x_2-x_1)^2+(y_2-y_1)^2+(z_2-z_1)^2}\)
Length BC = \(\sqrt{(x_3-x_2)^2+(y_3-y_2)^2+(z_3-z_2)^2}\)
Length AC = \(\sqrt{(x_3-x_1)^2+(y_3-y_1)^2+(z_3-z_1)^2}\)
Hence, AB = BC = AC
Therefore, points A,B,C make an equilateral triangle.