Rette perpendicolari
y = 2x		y = -1/2x
x	y
0	0
-1	-2
2	4
0	0
-2	1
4	-2
Rette parallele
y = 2x		y = 2x+2
0	0
-1	-2
1	2
0	2
-1	0
1	4