If A =2i + 2j + 3k, B =-i+2j+k and C=3i+j, then A +t B is perpendicular to C if t is equal to |...

If vec a=i+2j+k,vec b=2i+j and vec c=3i-4j-5k, then find a unit vector perpendicular to both of the vectors (vec a-vec b) and (vec c-vec b)

Given a=i+j-k, b=-i+2j+k" and "c=-i+2j-k . A unit vector perpendicular to both a + b and b + c is