MATH 235: Linear Algebra 2 Written Assignment 2 Fall 2022
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
MATH 235: Linear Algebra 2
Written Assignment 2
Fall 2022
Q1. Consider V = (y e R : y > 2) and the two operators on V :
y e - := y- _ 2(y + -) + 6, a o y := (y _ 2)a + 2,
for any y, - e V and any a e Q (the right hand sides of those equations are the standard calculations between real numbers. Verify that (V, e, o) is a vector space over the field Q.
Q2. (a) Prove that w1 = (l e d3x3(R) : l = _lT ) is a subspace of d3x3(R).
(b) Prove that w2 = (l e d3x3(R) : tr(l) = a11 + a22 + a33 = _1) is not a subspace of
d3x3(R).
Q3. (a) Let s = (y, y2 ) C P2(R) and w = ((y + 1)2 + 3y _ 1, 3y2 _ 2y + 5) . Which element of
w are in Span(s)? Justify your answer.
(b) Let s = (w1 , w2 , w3 ) be a subset of a vector space V over some field F. Prove that
Span(s) = (a1w1 + a2w2 + a3w3 : a1 , a2 , a3 e F) . (For this question, citing the result in Week02 lecture notes is not sufficient. Indeed, we are asking you to directly prove that example for the case n=3.)
Q4. Let V be a vector space over C and let w1 and w2 be two subspaces of V . Define the
summation of w1 and w2 as follows:
w1 + w2 := (w_ e V : w_ = z_1 + z_2 for some z_1 e w1 , z_2 e w2 ) . Similarly, we define the intersection of w1 and w2 to be
w1 n w2 := (w_ e V : w_ e w1 and w e w2 ) .
(a) Prove that w1 + w2 and w1 n w2 are both subspaces of V .
(b) Is w1 n w2 a subspace of V? If yes, prove it. If no, find a counter-example.
(c) Suppose w1 + w2 = V and w1 n w2 = () . Prove that for every vector w_ e V , there are unique vectors z_1 e w1 and z_2 e w2 such that w_ = z_1 + z_2 . (That is, for every vector w_ e V , there exist z_1 e w1 and z_2 e w2 such that w_ = z_1 + z_2 and if there are
vectors u_1 e w1 and u_2 e w2 such that w_ = u_1 + u_2 then z_1 = u_1 and z_2 = u_2 .) Q5. Let V be a vector space over a field F and let s1 and s2 be two subsets of V .
(a) Prove that if s1 C s2 then Span(s1 ) C Span(s2 ).
(b) Prove or disprove that Span(s1 n s2 ) = Span(s1 ) + Span(s2 ) (see the definition of the
summation in Question Q3.)
2022-09-23