Math 551 Section 01 Summer 2023 Session I
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Math 551 Section 01
Summer 2023 Session I
Chapter 1 Homework due Wednesday, June 7th at 11:59 PM
Notes: Try to answer all the questions by demonstrating all the steps of your cal- culations. Please submit your homework on Gradescope. This homework assignment covers Section 1 . 1, 1 .2 & 1 .3. Answer all the questions by demonstrating all the steps of your calculations. |
1. Recall Taylor’s theorem from Calculus: “Assume a function f (x) that has k + 1 derivatives in an interval [a, b], or simply, f e Ck+1 [a, b] and x0 e [a, b]. Then, for every x e [a, b], 3 ξ between x0 and x such that
f (x) = k (x - x0 )n + (x - x0 )k+1 ,
↗←
(1)
where Pk (x) is called the kth Taylor polynomial for f around x0 and Rk (x) is called the remainder, or truncation error. Note that
lim Pk (x)
→女
gives the Taylor series for the same function f about x = x0 and also a function f is analytic in (a, b) if the Taylor series equals f for all x e (a, b). Finally, the Taylor series around x = x0 三 0 is called MacLaurin series.
(a) (8 points) Find P1 (x), P2 (x) and P3 (x) around x0 = 0 if f (x) = x2 - 4x + 3. How P3 (x) is related to f (x)?
(b) (7 points) Same as part (a) but consider x0 = 1.
(c) (5 points) Given a polynomial f (x) with degree m, what can you say about f (x) - Pk (x) for k > m?
2. (15 points) Given the function f (x) = cos x, find both P2 (x) and P3 (x) about x0 = 0, and use them to approximate cos (0.1). Show that in each case the remainder term provides an upper bound for the true (absolute) error.
3. Consider the function f (x) = ex .
(a) (10 points) Find the MacLaurin series of the function f (x) = e , ix .e., the Taylor series about x0 = 0 (write separately Pk (x) and Rk (x)),
(b) (10 points) Find a minimum value of k necessary for Pk (x) to approximate f (x) to within 10亿6 on the interval [0, 0.5] (here, you must use the remainder term).
4. (5 points) Let f (x) = ex and the remainder of it is 5th- degree Taylor series about x0 = 0 is given by
R5 (x) = eξ ,
for x e [- , ], where ξ is between x and 0, find an upper bound for |R|, valid for
5. (10 points) Use Taylor’s Theorem to show that
(1 + x)亿1 = 1 - x + x2 + 0(x3 )
for x sufficiently small.
6. (10 points) Use Taylor expansions for f (x 土 h) to derive an 0(h2 ) accurate approxi- mation to the second derivative f\\ (x) using f (x) and f (x土h). Provide all the details of the error estimate.
7. MATLAB
(a) (10 points) Using the m-file taylor q3.m, plot the function f (x) = ex and its Taylor polynomials about x0 = 0, p2 , p4 and p6 . Run the script and show the graphs.
(b) (10 points) Modify the m-file abs errors.m with initial step-size h = 0.15 and N = 10, provide the absolute errors and graph.
2023-06-06