I'm sure u know forces and it's meaning but i just want to make sure u kno following :
when two forces act in the same straight line (nasf il itijah ..... mithil 2ai parallel lines ) then u get the resultant force by adding the two forces.
but as for the parallelogram , the resultant force is the diagonal of the parallelogram ...here is the rule from my book :
Oh sure thing np ..wait a sec so that i get the book.
In my book it says :
if the two forces acting at a point are represented in size and direction by the sides of a parallelogram drawn from the point ,their resultant is represented in size and direction by the diagonal of the parallelogram drawn from the point.
I hope u got it , if u didn't let me kno.