When doing matrix elimination (Gauss method) the row space and the column spaces

When doing matrix elimination (Gauss method) the row space and the column spaces of the initial matrix are changed. How do they change? How is the “column picture” changed after each step of elimination? How is the “row picture” changed after elimination? (The terms “column picture” and “row picture” can be found in page 34 of Strang, Gilbert. Introduction to Linear Algebra. 4th ed. Wellesley-Cambridge Press, 2009. ISBN: 9780980232714)

When doing matrix elimination (Gauss method) the row space and the column spaces

When doing matrix elimination (Gauss method) the row space and the column spaces of the initial matrix are changed. How do they change? How is the “column picture” changed after each step of elimination? How is the “row picture” changed after elimination? (The terms “column picture” and “row picture” can be found in page 34 of Strang, Gilbert. Introduction to Linear Algebra. 4th ed. Wellesley-Cambridge Press, 2009. ISBN: 9780980232714)

Section 5.2: # 4, 7, 12, 13, 16, 21. Section 5.3: # 3, 9, 15, 19, 20. Section 5.

Section 5.2: # 4, 7, 12, 13, 16, 21.
Section 5.3: # 3, 9, 15, 19, 20.
Section 5.4: # 5, 6, 15, 16.
See attached file for questions MAKE SURE TO SOLVE IN STEPS
Hints:
Section 5.3:
#19. To obtain QR factorization, you need to apply Gram-Schmidt process for column vectors of A first. What happens if A is an orthogonal matrix?
#20. Note that det(QR) = det(Q)det(R).
Section 5.4:
#15. A matrix is orthogonally diagonalizable if and only if it is symmetric. So, you can prove that AB is symmetric.
#16. Orthogonally diagonalize the matrix A first. Note that a diagonal matrix D has all nonnegative entries of its diagonal if and only if D=M^2 for some diagonal matrix M.