u = <3,5>
v = <-2, 1>
if two vectors are parrallel, then:
u= kv, where k is some constant.
<3,5>= k<-2,1>
for values of x:
3= -2k
k= -3/2
for values of y:
5= (1)k
since k for x does not equal to k for y, the two vectors are not parrallel.
note: you could also use a dot product to check this