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Linear Algebra, Theory And Applications, 2012a

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72 MATRICES AND LINEAR TRANSFORMATIONS<br />

5. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of 2π/3.<br />

6. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of π/12. Hint: Note that π/12 = π/3 − π/4.<br />

7. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of 2π/3 and then reflects across the x axis.<br />

8. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of π/3 and then reflects across the x axis.<br />

9. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of π/4 and then reflects across the x axis.<br />

10. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of π/6 and then reflects across the x axis followed by a reflection across the<br />

y axis.<br />

11. Find the matrix for the linear transformation which reflects every vector in R 2 across<br />

the x axis and then rotates every vector through an angle of π/4.<br />

12. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of π/4 and next reflects every vector across the x axis. Compare with the<br />

above problem.<br />

13. Find the matrix for the linear transformation which reflects every vector in R 2 across<br />

the x axis and then rotates every vector through an angle of π/6.<br />

14. Find the matrix for the linear transformation which reflects every vector in R 2 across<br />

the y axis and then rotates every vector through an angle of π/6.<br />

15. Find the matrix for the linear transformation which rotates every vector in R 2 through<br />

an angle of 5π/12. Hint: Note that 5π/12 = 2π/3 − π/4.<br />

16. Find the matrix for proj u (v) whereu =(1, −2, 3) T .<br />

17. Find the matrix for proj u (v) whereu =(1, 5, 3) T .<br />

18. Find the matrix for proj u (v) whereu =(1, 0, 3) T .<br />

19. Give an example of a 2 × 2 matrix A which has all its entries nonzero and satisfies<br />

A 2 = A. A matrix which satisfies A 2 = A is called idempotent.<br />

20. Let A be an m × n matrix and let B be an n × m matrix where n

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