Question

what happends when two planes intersect

Answer 1

you get a line

plane 1: x+y+z = 1 --- > z = 1-x-y
plane 2: 2x -y +z = 3 --> z = 3 -2x+y

intersection:
1-x-y = 3-2x+y ---> y = (1/2)x -1 (line)