3. Prove or disprove the following statements: (a) Let U, WE R" with w / 0, projo(-U) = - proju(U). (b) Let U, we R" with w / 0 and c E R, perp,(cv) = cperp.(7). 4. Let u, U E R3 (a) Let u = b some a, b E R. Find all possible values of a and b such that u and of are orthogonal to each other and ||6]) = 3v3. (b) Determine all the unit vectors that are orthogonal to both of the vectors listed below: - N