A square matrix A is idempotent if A² = A. Let V be the vector space of all 2 x 2 matrices with real entries. Let H be the set of all 2 x 2 idempotent matrices with real entries. Is H a subspace of the vector space V? 1. Is H nonempty? choose 2. Is H closed under addition? If it is, enter CLOSED. If it is not, enter two matrices in H whose sum is not in H, using a comma separated list and syntax such as 1 2 [[1,2], [3,4]], [[5,6], [7,8]] for the answer CO ∞ 2 6 5 (Hint: to show 3 4 7 that H is not closed under addition, it is sufficient to find two idempotent matrices A and B such that (A + B)² ‡ (A + B).) 8 3. Is H closed under scalar multiplication? If it is, enter CLOSED. If it is not, enter a scalar in R and a matrix in H whose product is not in H, using a comma separated list and syntax such 3 4 as 2, [[3,4], [5,6]] for the answer 2, (Hint: to show that H is not closed 6 under scalar multiplication, it is sufficient to find a real number r and an idempotent matrix A such that (rA)2 # (rA).) 4. Is H a subspace of the vector space V? You should be able to justify your answer by writing a complete, coherent, and detailed proof based on your answers to parts 1-3. choose

Linear Algebra: A Modern Introduction
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Chapter5: Orthogonality
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A square matrix A is idempotent if A² = A.
Let V be the vector space of all 2 x 2 matrices with real entries. Let H be the set of all 2 x 2
idempotent matrices with real entries. Is H a subspace of the vector space V?
1. Is H nonempty?
choose
2. Is H closed under addition? If it is, enter CLOSED. If it is not, enter two matrices in H whose
sum is not in H, using a comma separated list and syntax such as
1 2
[[1,2], [3,4]], [[5,6], [7,8]] for the answer
5 6
(Hint: to show
8
3 4 7
that H is not closed under addition, it is sufficient to find two idempotent matrices A and B
such that (A + B)² ‡ (A + B).)
2
3. Is H closed under scalar multiplication? If it is, enter CLOSED. If it is not, enter a scalar in R
and a matrix in H whose product is not in H, using a comma separated list and syntax such
3 4
as 2, [[3,4], [5,6]] for the answer 2,
(Hint: to show that H is not closed
6
under scalar multiplication, it is sufficient to find a real number r and an idempotent matrix A
such that (rA)2 # (rA).)
4. Is H a subspace of the vector space V? You should be able to justify your answer by writing
a complete, coherent, and detailed proof based on your answers to parts 1-3.
choose
Transcribed Image Text:A square matrix A is idempotent if A² = A. Let V be the vector space of all 2 x 2 matrices with real entries. Let H be the set of all 2 x 2 idempotent matrices with real entries. Is H a subspace of the vector space V? 1. Is H nonempty? choose 2. Is H closed under addition? If it is, enter CLOSED. If it is not, enter two matrices in H whose sum is not in H, using a comma separated list and syntax such as 1 2 [[1,2], [3,4]], [[5,6], [7,8]] for the answer 5 6 (Hint: to show 8 3 4 7 that H is not closed under addition, it is sufficient to find two idempotent matrices A and B such that (A + B)² ‡ (A + B).) 2 3. Is H closed under scalar multiplication? If it is, enter CLOSED. If it is not, enter a scalar in R and a matrix in H whose product is not in H, using a comma separated list and syntax such 3 4 as 2, [[3,4], [5,6]] for the answer 2, (Hint: to show that H is not closed 6 under scalar multiplication, it is sufficient to find a real number r and an idempotent matrix A such that (rA)2 # (rA).) 4. Is H a subspace of the vector space V? You should be able to justify your answer by writing a complete, coherent, and detailed proof based on your answers to parts 1-3. choose
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