Given the following vector:

a= i + 2j -2k

Find a possible set of values for y and z such that the unit vector shown below is perpendicular to vectora.

b= (y)j + (z)k

I've tried using both of these rules [ (i) |axb| = |a||b|sin90 (ii)a.b= 0 ]to form an equation but i can't seem to get an answer.

I suspect it has something to do with matrices also, as this is part of a matrices question.