Homework Assignment 4
Limits

Please submit the answers to the following in electronic format, either TeX, Word or PDF.

(Be as rigorous and precise as you can!)


  1. Show that limx → 0 sin(x)/x = 1, using the ε-Δ proof.
    [Hint]

  2. Using the result of the previous problem, show that limx → 0 sin(sin(x))/x exists
    [Hint]

  3. Show that limx → 0 sin(1/x) does not exist using the ε-Δ proof.
    [Hint]

  4. Show that as x → ∞ [√(x+1)-√(x)] = 0
    [Hint]

  5. Show that the Fibonacci sequence of numbers 1,1,2,3,5,8,13, given by the relationship an+1=an+an-1 satisfies

    [Hint]

    Given this recursion relation, find the asymptotic limit of an as n → ∞. This means find a c and an r such that

    limn → ∞ an/(crn) = 1

  6. Show that one can compute π by the infinite series

    π = 4*(1-1/3+1/5-1/7+1/9-1/11+1/13-1/15+1/17-...)
    =∑0 (-1)n 1/(2n+1)
    that is from the sum of the alternating series of reciprocals of odd numbers.
    [Hint]

    Extra Credit; Derive as many of the series representations for Pi as you can. There are 43 of them listed in this reference!

  7. Show that the non-alternating series ∑n=1n=∞ 1/(2n+1) diverges, that is, becomes infinite.
    [Hint]

  8. In the section "Archimedes the Numerical Analyst" in the reference Archimedes There is a procedure to calculate π to 18 decimal places strictly from inscribed and circumscribed regular polygons of 3, 6, 12, 24, 48, and 96 sides respectively. Carry out this procedure, steps 1-7, or this reference and show that it is correct.

    See this reference (Section 1.3) for the correct relationship
    [Hint]

  9. Define the Heaviside function as
    H(t) = 0 if t < 0,
    and
    H(t) = 1 if t >= 0
    Show, using an ε-Δ proof that the limit of H(t) as t → 0 does not exist.
    [Hint]

  10. Show that
    lim x → 0+ xx = 1

    lim x → 0+ means that x approaches zero, but only takes on positive values...
    [Hint]