11. (Strang 4.2.21, 22, 28) Consider a matrix A with linearly independent columns and its projection matrix, P = A(AT A)-'A". (a) Prove that P² = P, by multiplying P by itself and simplifying. (b) Prove that P is symmetric, by computing P"; recall that the inverse of a symmetric matrix is also symmetric. (c) Use the results of (a) and (b) to prove that the diagonal entry P22 must always be equal to the square of the length of the second column of P.

Advanced Engineering Mathematics
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11. (Strang 4.2.21, 22, 28) Consider a matrix A with linearly independent columns and its
projection matrix, P = A(AT A)-'A".
(a) Prove that P² = P, by multiplying P by itself and simplifying.
(b) Prove that P is symmetric, by computing P"; recall that the inverse of a symmetric
matrix is also symmetric.
(c) Use the results of (a) and (b) to prove that the diagonal entry P32 must always be
equal to the square of the length of the second column of P.
Transcribed Image Text:11. (Strang 4.2.21, 22, 28) Consider a matrix A with linearly independent columns and its projection matrix, P = A(AT A)-'A". (a) Prove that P² = P, by multiplying P by itself and simplifying. (b) Prove that P is symmetric, by computing P"; recall that the inverse of a symmetric matrix is also symmetric. (c) Use the results of (a) and (b) to prove that the diagonal entry P32 must always be equal to the square of the length of the second column of P.
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