MAT 150C HW 2
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MAT 150C HW 2
Problem 1. Suppose λ is an eigenvalue of a linear transformation T : V → V . Show that λk is an eigenvalue of Tk (without assuming that T is diagaonlizable) .
For the next two problems, we let V be a finite dimensional complex vector space and let {vi } be a basis of V . Then every element v ∈ V can be written uniquely as a linear combination 对 ai vi . For each 1 ≤ i ≤ n, define a map
αi : V → C
v = 工 ai vi '→ ai
i
Problem 2. Prove that αi is a linear functional (i. e ., an element of V*) .
Problem 3. Prove that {αi } is a basis of V* . (Hint: you need to show linear independence and spanning.) Problem 4. Prove that V ⊂ (V* )* (without assuming that V is finite dimensional) . Deduce that if V is finite dimensional, then V = (V* )* . (Hint: for the second claim, it is enough to use Problem 3 to argue that dim(V* )* = dimV .)
Problem 5. Let V and W be two complex vector spaces . Let Hom(V,W) be the set of linear transformations from V to W . Define addition and scalar multiplication on Hom(V,W) and show that it is a vector space .
For the next three problems, we let V and W be two finite dimensional vector spaces with bases {vi } and {wj }, respectively. Let {αi } be the basis of V* defined in Problem 3. For any 1 ≤ i ≤ n and 1 ≤ j ≤ m, we define
fij : V → W
v → αi (v)wj .
Problem 6. Prove that fij is a linear transformation. (Hint: you need to show that it preserves addition and scalar multiplication.)
Problem 7. Let f : V → W be a linear transformation. Show that there exists mn many complex numbers cij with 1 ≤ i ≤ n and 1 ≤ j ≤ m such that f = 对ij cij fij .
Problem 8. Prove that V* ⊗W Hom(V,W) . (Hint: let Φ : V* ⊗W → Hom(V,W) be the map defined by
Φ (对i,j cij αi ⊗ wj ) = 对i,j cij fij . Prove that Φ is a linear map . Note that a surjective linear map between
vector spaces of the same dimension is automatically bijective for dimension reasons .)
Problem 9. Let V and W be two finite dimensional vector spaces . Let {vi } and {v} be two bases of V and let {wj } and {w} be two bases of W . Suppose v = 对k aki vk and w = 对l blj wl for all i and j . Find the change of basis matrix relating the basis {v ⊗ w} to the basis {vi ⊗ wj } of V ⊗ W .
Problem 10. Compute the character of the 3- dimensional representation of S3 (the one where σ acts by σ(ei ) = eσ(i)) by writing down the character value for each conjugate class .
2023-04-19