7. (1 mark) Let x] = (1,1,1) and x2 = (3, - 1,4) ]: A. Do x and x2 span R3? Explain. B. Let x3 be a third vector in R'and set X = (X] X2 X3) . What condition(s) would X have to satisfy in order for x1, x2, and x3 to form a basis for R3 ? C. Find a third vector x3 that will extend the set {x1,X2} to a basis for R3