Please help. Given the 3 vectors a = -21 + 3j - k, b = 41 - j + 2k and c = -3i + 2j - 3k: 1. Find the unit vector perpendicular to a and b + c. 2. Evaluate a . b x c I'm completely clueless on how to approach the first question. Any help would be great. I'm not sure which product I'm meant to perform first in the second question. Also, 3. p1 and p2 are planes with cartesian equations 2x - y + 3z = 5 and x - 3y + z = -2, respectively, and l is the line of intersection of p1 and p2. Find a vector v parallel to l. I've already determined the normals of both planes: for p1 : 2i - j + 3k and for p2 : i - 3j + k, but I'm not sure where to go from here. Clearly v will be perpendicular to both normals, but I don't know how to find that vector. Any help for these questions would be greatly appreciated.