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MATH1115 ASSIGNMENT
DUE MONDAY MARCH 27 AT 11PM Homework Policy The following rules apply to collaboration and the use of outside resources: • Collaboration with other students is allowed – encouraged, in fact – but if you collaborate with other students you must acknowledge the collaboration in writing at the top of your assignment. For example, “On problems 1 and 4 I benefitted from conversations with John Doe, and my solution to problem 5 was obtained in collaboration with Jane Doe.” Assignments without a collaboration statement will not be graded. • The use of outside resources is also permitted, but be careful. For example, you are allowed to read about Venn diagrams on Wikipedia. You are not allowed to read the solution to an assignment problem someone posted on Stackexchange. If in doubt, ask before you look. Any such use must also be acknowledged in writing in the assignment. • Unless otherwise noted, the problems should be solved without the assis- tance of computer software. • Regardless of which sources you use, the writing of all solutions must be your own. Note that this is only half of the assignment. The other half is a MATLAB Grader assignment. (0) (a) Write a collaboration statement, detailing who you worked with and any outside resources you may have used. (You don’t need to mention help you received from the lecturers, your demonstrator, or the drop-in centre.) This part is mandatory. (b) Write a reflection on how the course is going. Did you go to lectures, and to your workshop? Did you spend time with a study group, or use any of the other resources (like the drop-in centre or office hours) that are available to you? How much time did you spend on the course in the past week? This part is optional. (1) (4 points) Suppose that A,B are non-empty subsets of R. Show that if A ⊂ B and B is bounded from above, then supA exists and supA ≤ supB. (2) (7 points) (a) (3 points) Let f : R → R be a function which is continuous at x = 0. Use the definition of differentiability to prove that the function g : R → R defined by g(x) = x(f(x)) is differentiable at x = 0 and find g′(0). 1 2 MATH1115 ASSIGNMENT 5, DUE MONDAY MARCH 27 AT 11PM (b) (4 points) Again using the definition of the derivative, calculate the derivative of f(x) = 12+5x on its natural domain (−∞,− 25 )∪(− 25 ,∞) = R\{− 25}. You may not use any differentiation rules (like the product rule, the quotient rule, etc). (3) (4 points) The final calculus question will be posted after the Modelling Workshop on Thursday, 23/3. (4) (3 points) Without computing any inverse matrices, solve the following equation for X: X · 2 5 1 3 42 11 −165 13 6 13 −12 22 7 17 6 5 = 2 5 1 3 42 11 −165 13 8 18 −11 25 1 2 3 −4 (5) (Total of 8 points) Recall that the transpose AT of a matrix is defined by interchanging the rows and columns: (AT )ij = Aji. We say a square matrix A is skew symmetric if AT = −A. (a) (2 points) Show that whenever AB is defined, BTAT is also defined and (AB)T = BTAT . (For this part A and B do not have to be skew symmetric.) (b) (3 point) If A = b cf is a skew symmetric 3 × 3 matrix, what are the remaining entries of A? Is A invertible? (Your answer may depend on b, c and f .) (c) (3 points) Show that if A is skew symmetric and invertible then A−1 is also skew symmetric. (To be clear: A is not the 3 × 3 matrix from part (b) but rather a skew symmetric matrix of arbitrary dimension.) (6) (4 points) Prove that there is exactly one degree at most 2 polynomial p(x) = a0+a1x+a2x 2 passing through 3 points (x1, y1), (x2, y2) and (x3, y3) as long as x1, x2 and x3 are distinct. (You may now use determinants if you want to.)