Hey, I was wondering if someone could help me sort out how to think about this:

Find the parametric equation of the line throughp= (2, -5) andq= (-3, 1).

I have no problem seeing how the line is parallel to (q-p), but the key then givespas the constant in the parametric equation without further comment, so if t is the parameter we have

M =p+ (q-p)t

My question is, how exactly do we know to usephere? I feel like I'm missing something basic, any help would be greatly appreciated!