Intersection point of 2 vectors in R3

Hi everyone,

i'm not quite sure where this thread should go but here i go.

I have 2 vectors

Here are the 2 points for vector 1 (in R3)

V1 : $\displaystyle A (-3,0,-4) and B(a,a,5) $

Here is the symetric equation of vector 2

V2 : $\displaystyle (x+3)/2 = y-1 = (z+2)/a$

My parametric equations for those 2 vectors should be :

V1: $\displaystyle

x = -3 +(a+3)s

y = as

z = -4 + 9s

$

V2: $\displaystyle

x = -3 + 2t

y = 1 + t

z = -2+ at

$

My problem is that I need to find the unknown a in order for my 2 vector to have one intersection point. I'm missing something but i cannot pinpoint what... and this is driving me nuts. Finding V1 // V2 is easy as well as V1 perpendicular to V2 but i'm missing something obvious.

any help would be appreciated.