Determine if each of the following sets of vectors U is asubspace of the specified vector space, and if so, describe the setgeometrically:
(a) U ? R2, where U = {?x1,x2? : x1 = 0}
(b) U ? R2, where U = {?x1,x2? : x1x2 = 0}
(c) U?R3,whereU={?x1,x2,x3?:?1,2,3?·?x1,x2,x3?=0}
(d) U ? R3, where U = {?x1,x2,x3? : ?1,2,2? · ?x1,x2,x3? = 0and
?1, 3, 0? · ?x1, x2, x3? = 0}
