hello thanx for the solution

i tried to solve by resolving the velocites in the two directions

i took a general angle between the two particles as

 

 in the horizontal dirction

 distance travelled by
B in time t is ut              ...........................( if t is time after wich they meet)

 

thefore for point A

 

_{[ 0]}^{[t ]} v cos  dt  = ut

 

hence

_{[ 0]}^{[ t]} cos  dt = ut/v

 

in the vertical direction

relative velocity is v - u cos

 

l =

_{[ 0]}^{[ t]} v - u cos  

 

after solving and then substituing

we get

l = vt - u (ut/v)

 

then

t = lv / (v2 - u2)

 

is the method right??