Q4. Find all solutions of 91x² + y² = 1 with x, y Є Z.

Q3. Find all solutions of x² - 29y² = ±1 with x, y ɛ Z.

Problem 11 (Gram-Schmidt). Try the Gram-Schmidt procedure for the vectors, 1 0 2 with respect to the standard dot product on R4. What happens? Can you explain why you are unable to complete the algorithm? Problem 12 (Orthogonal Matrices Preserve Orthogonality). Suppose x, y = Rn" are orthogonal to each other with respect to some inner product (.,.) and that A is an orthogonal matrix and B is some invertible matrix. 1. Prove that Ax and Ay are also orthogonal to each other and that ||x|| = ||Ax|| and ||y|| : = ||Ay||. 2. Is it true that Bx and By are also orthogonal to each other and that ||x|| = ||Bx|| and ||y|| = = ||By||? Provide a proof or a counter-example. Problem 13 (Orthogonal Complement). Let W be the subspace of R5 spanned by, 1 2 2 4 u = 3 , v= 7 2 2 Find a basis of the orthogonal complement W- of W. Verify in this particular example that WW₁ = {0} and that dim(W) + dim(W¹) = 5.

Problem 5 (Rank-Nullity Theorem). Let T : P3 → M2×2 be defined as, T(p(x)) P(0) p'(1)] = 1. Prove that T is a linear transformation. 2. Find ker(T). Is T injective? 3. Find im(T). Is T surjective? 4. Verify the Rank-Nullity Theorem for T. Problem 6 (Change of Basis). Let B₁ = polynomials in P3. - - {1, x, x², x³} and B₁ = {1, x, x(x − 1), x(x − 1)(x − 2)} be two sets of 1. Is B2 a basis for P3? Justify your answer. 2. Find SB₁→B₂ and SB2→B₁. Which one is "easier" to find? - Problem 7 (Change of Basis). Let B₁ = {eª, sin² (x), cos² (x)} and B₁ = {e*, sin(2x)}. Recall that sin(20) = 2 sin(0) cos(0). Suppose V = span (B₁) and W = span(B2). Let T: VW be a linear transformation defined as T(f(x)) = f'(x). 1 1. Prove that B₁ is a basis. 2. Let g(x) = 5 - 3e. Show that g = V and find T(g(x)). 3. Find [TB₁B2 4. Is T injective? 5. Is T surjective?

Problem 14 (Orthogonal Matrices). Prove each of the following. 1. P is orthogonal PT is orthogonal. 2. If P is orthogonal, then P-1 is orthogonal. 3. If P, Q are orthogonal, then PQ is orthogonal. Problem 15 (Orthogonal Complement). Consider P2 with the inner product, (f,g) = f(x)g(x)dx. Put W = span(2x+1). Find a basis of W. (1)

Problem 8 (Diagonalization). Let T : P₂ → P₂ be defined as, T(p(x)) = xp'(x). 1. Find the eigenvalues and eigenvectors of T. 2. Show that T is diagonalizable and write P2 as the sum of the eigenspaces of T. Problem 9 (Basis). Determine all the values of the scalar k for which the following four matrices form a basis for M2×2: A₁ = , A2 = k -3 0 , A3 = [ 1 0 -k 2 0 k " A₁ = . -1 -2 Problem 10 (Orthogonality). In this question, we will again see how orthogonality makes computations sim- pler. 1. Let u1,..., un be an (ONB) of a finite-dimensional inner product space V. Let v = c₁u₁ + ... + Сnun and w = d¹µ₁ + ... + dnUn be any two elements of V. Prove that (v, w) = c₁d₁ + ... + Cndn. 2. Write down the corresponding inner product formula for an orthogonal basis.