The formula for calculating the distance between two points is:
#d = sqrt((color(red)(x_2) - color(blue)(x_1))^2 + (color(red)(y_2) - color(blue)(y_1))^2 + (color(red)(z_2) - color(blue)(z_1))^2)#
Substituting the values from the points in the problem gives:
#d = sqrt((color(red)(1) - color(blue)(-1))^2 + (color(red)(1) - color(blue)(-1))^2 + (color(red)(1) - color(blue)(-1))^2)#
#d = sqrt((color(red)(1) + color(blue)(1))^2 + (color(red)(1) + color(blue)(1))^2 + (color(red)(1) + color(blue)(1))^2)#
#d = sqrt(2^2 + 2^2 + 2^2)#
#d = sqrt(4 + 4 + 4)#
#d = sqrt(12)#
#d = sqrt(4 * 3)#
#d = sqrt(4)sqrt(3)#
#d = 2sqrt(3)#
Or
#d ~= 3.464#