If lines are parallel, slopes are equal
If lines are perpendicular, the product of the slopes is -1.
The formula to find the slope is
1)
Here P (a, b) & Q(c,d)
Slope of PQ
Also P'(-b, a) & Q'(-d,c)
Solpe of P'Q'
Now slope of PQ × Slope of P'Q'
As the product of slopes = -1.
PQ & P'Q' are perpendicular to each other.
2)
P(w,v), Q(x,z)
Slope of PQ
P'(w+a, v+b), Q' (x+a, z+b)
Slope of P'Q'
Hence slope of PQ = Slope of P'Q'
Hence PQ is parallel to P'Q'