How do I check whether two vectors are collinear

I know I can compare it using graph but how do I determine it theoretically?

Two vectors are collinear if their cross product is zero. Meaning no work is done on one vector by the other.

Let vectors a = (a1,a2,.....,an), and b=(b1,b2,b3,...bn).
a & b are collinear iff whenever ai =0, then bi = 0, and for the non zero components, a1/b1 = a2/b2 =....=an/bn.