MATH203-21S1 Linear Algebra
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Final Exam
MATH203-21S1
Linear Algebra
1. [15 marks]
(a) Suppose B is a 3 × 4 matrix with rank k .
i. Is it possible that the equation Bx = b has a unique solution?
ii. What would the columns of B look like if k = 0?
iii. What would the columns of B look like if k = 1?
iv. If null(B) is a (1-dimensional) line in R4 , what does col(B) look like?
v. Give a geometric description of null(B) and col(B) when k = 2.
(b) Let A = -;
'2 1 -3'.
i. Give a basis for the null space of A.
ii. Find a vector v e R3 such that v e\ col(A). You must justify your answer.
iii. Prove that for any u e R3 , if the vectors Ae1 , Ae2 , and u are linearly dependent then u e col(A)
iv. Find a basis for the subspace in R3 of vectors v such that Av = v.
v. Find an invertible matrix P such that AP = PD for some diagonal matrix D, or show explain why no such matrix exists.
2. [12 marks]
-1; -1; --1; -0;
Let U = span '''''' , '''''' and V = span '''11-1''' , '''''' in R4 .
(a) Show that U and V are orthogonal complements.
(b) Find an orthogonal basis for V .
(c) Compute proj↓ (e1 ) and proj↓ (e4 ).
(d) Suppose C is the 4 × 4 matrix representing the linear map L : R4 → R4 determined by L(x) = proj↓ (x). You do not need to compute C .
i. C has eigenvalues λ = 0, 1. What are the corresponding eigenspaces?
ii. Is C symmetric?
(e) Suppose C\ is the 4 × 4 matrix representing the linear map sending x to 3projU (x). Is C + C\ invertible? Justify your answer.
3. [10 marks]
Consider the inner product space V = c[0, 1] of continuous real valued functions defined on the closed interval [0, 1], with inner product given by
(f, g) = |0 1 f (x)g(x)dx .
Let f0 (x) = 1, f1 (x) = x in V .
(a) Find the magnitude of f0 (x).
(b) Find the orthogonal projection of f1 (x) onto f0 (x).
(c) Find a function h(x) e V that is orthogonal to f0 (x).
(d) Let W = span{f0 (x), f1 (x)} c V .
i. Find an orthogonal basis of W .
ii. Why is the map L : W → W defined by L(g(x)) = g\ (x) a linear map?
iii. Write down the matrix of L with respect to a basis of W (make sure to state the basis you are using!).
4. [10 marks]
Determine whether the following statements are true or false. Give a justification for your answer.
(a) If two nonzero vectors in an inner product space are orthogonal, then they are linearly independent.
(b) If the vectors v1 , v2 , v3 are linearly dependent, then one of them is a scalar multiple of another.
(c) If A is an m × n matrix of rank m, then AT A is invertible.
(d) Suppose λ = 0 is an eigenvalue of the square matrix B . Then the equation Bx = 0 has infinitely many solutions.
(e) Suppose A is the 2×3 matrix A = ! – !'(-)
i. e1 lies in the row space of A.
ii. – !1(1) lies in the column space of A.
iii. 36 is an eigenvalue of AT A.
(f) Linear algebra is useful and interesting.
0
1/,2
1/,2
1/2 ;
-1/,2'.
2022-06-14