Question

what do lines like this || mean in geometry

Answer 1

means "parallel to"

e.g. AB || CD means "line AB is parallel to line CD"

Answer 2

ps What does mean

Answer 3

need a refresh lol

Answer 4

Perpendicular to.

Answer 5

┴ means "is perpendicular to"
e.g. AB ┴ CD means "line AB is perpendicular to line CD"

Answer 6

THank you Guys :)

Answer 7

Perpendicular = 90 degree = pi/2 radian
If 2 lines perpendicular : their product of slope m1 * m2 = -1
There're quite a few of interesting application about 90 degree as Pythagorean theorem!