Indicate whether each statement is always true or sometimes false. Justify your answer by giving a logical argument or a counterexample.
(a) If ||u + v ||2 = ||u||2 + ||v||2 then u and v are orthogonal.
(b) If u is orthogonal to v and w, then u is orthogonal to v + w
(c) If u is orthogonal to v + w, then u is orthogonal to v and w.