[a b (e) Let B = be any 2 x 2 matrix. [cos a = u11 [sin a (i) Show that there are real numbers un and a such that Hint: erpress as a scalar multiple of a unit vector, and hence find an erpression for u in terms of a and c. (ii) Let a e R. Use the invertibility of R, to prove that there are unique U12, U22 € R such that -- sin a cos a [cos a u12 + u22 (sino [sin a] (iii) Use parts (i) and (ii) to show that B can be expressed in the form B = R,U for some a €R and some upper-triangular matrix U. (iv) Suppose that B = RU = R3V, where a, B e R and U and V are upper- triangular. Prove that if B is invertible, then U = ±V. %3D

Linear Algebra: A Modern Introduction
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Chapter5: Orthogonality
Section5.3: The Gram-schmidt Process And The Qr Factorization
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(e) Let B =
be any 2 x 2 matrix.
COS a
(i) Show that there are real numbers un and a such that
u11
sin a
Hint: erpress
as a scalar multiple of a unit vector, and hence find an
erpression for un in terms of a and c.
(ii) Let a € R. Use the invertibility of R, to prove that there are unique
u12, U22 €R such that
cos a
= u12
- sin a
+ u22
cos a
sin a
(iii) Use parts (i) and (ii) to show that B can be expressed in the form
B = R,U
for some a €R and some upper-triangular matrix U.
(iv) Suppose that B = R,U = R3V, where a, B eR and U and V are upper-
triangular. Prove that if B is invertible, then U = ±V.
Transcribed Image Text:(e) Let B = be any 2 x 2 matrix. COS a (i) Show that there are real numbers un and a such that u11 sin a Hint: erpress as a scalar multiple of a unit vector, and hence find an erpression for un in terms of a and c. (ii) Let a € R. Use the invertibility of R, to prove that there are unique u12, U22 €R such that cos a = u12 - sin a + u22 cos a sin a (iii) Use parts (i) and (ii) to show that B can be expressed in the form B = R,U for some a €R and some upper-triangular matrix U. (iv) Suppose that B = R,U = R3V, where a, B eR and U and V are upper- triangular. Prove that if B is invertible, then U = ±V.
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