QUESTION 5 Please EXPLAIN BRIEFLY

Kar; n is a real vector space with respect to the usual addition and scalar multiplication. 4. Recall that M, (R) is the real vector space of all n x n real matrices. Now, prove that W1 = {A EMn (R) : AT = A}, W2 = {A E Mn (R) : AT = -A} and W3 = {A E Mn (R) : A is upper triangular}, are subspace of M, (R). 5. (T) Which of the following are subspaces of R3: (a) {(x, y, z) | x20}, (b) { (x, y, z) | xty = z}, (c) {(x, y, 2) [ x = y?)