how do you determine which ones are unit vectors?

Question

0.9 0.28 6/5 -16/65
0.1 0.96 -1/5 63/65

Answer 1

Calculate the length:

for a vector (a b c d) = sqrt(a²+b²+c²+d²).

(to check for unity, you can drop the sqrt)

0.9*0.9 + 0.28 * 0.28 + 6/5*6/5 + 16/65*16/65 = 2.33...

0.1*0.1 + 0.96*0.96 + 1/5*1/5 + 63/65*63/65 = 1.911...

So these are not unit vectors.

If you divide the vector by its length you will get unit vectors.

Answer 2

This appears to be a 4 dimensional vector
Square each number add the results together and if the result is one then the vector is a unit vector.