Solutions

HOW TO FIND THE ANGLE BETWEEN TWO LINES

  x =  y =  z and
- x =  - y = z 

1st Rewrite these equations in standard forms

  (x -0)/1 =  (y-0)/1   = (z-0)/1  and

(x-0)/(-1) = (y-0)/(-1) = (z -0)/(1)

Direction ratios  of 1st line are (1 , 1 , 1) and Direction  ratios of 2nd line are (-1,  -1 , 1);

Using formula cosθ = -1/3

Now  θ =  cos^-1 ( -1/3)