Monday, April 23, 2012

Practice Exam 1

Practice Exam 1
Made on 20120417. Distributed in class on 20120417. Made available online on 20120423.

#1) Evaluate the integral.
\[
\int\frac{6x+1}{(x+1)(2x-1)}dx
\]

#2) Find the area of the region enclosed by one loop of the curve.
\[
r=3\sin\left(3\theta\right)
\]


#3) Determine whether the integral is convergent or divergent. If
it is convergent, evaluate it.
\[
\int_{e}^{\infty}\frac{1}{x\left(\ln x\right)^{2}}dx
\]


#4) Determine whether the following are convergent or divergent.
State the type of test you use. You may use each type of test only
once.

a)
\[
\sum_{n=2}^{\infty}2\frac{3^{n}}{4^{n-1}}
\]

b)
\[
\sum_{n=2}^{\infty}\frac{\sin\left(n\pi\right)}{\log n}
\]
20120426: Changed the starting term from $1$ to $2$.

B)
\[
\sum_{n=2}^{\infty}\frac{\cos\left(n\pi\right)}{\log n}
\]
20120426: Added this problem, because the original b) was somewhat trivial.

c)
\[
\sum_{n=1}^{\infty}\frac{n^{2}}{n+1}
\]


d)
\[
\sum_{n=1}^{\infty}\frac{n^{n}}{\left(2+n^{2}\right)^{n}}
\]


e)
\[
\sum_{n=1}^{\infty}\frac{1+2n}{3n^{3}}
\]


#5) There should be three forms/strategies from section 11.7 which
you didn't use. State them.

22 comments:

  1. Replies
    1. This is a geometric series. Can you evaluate the value of the series?

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  2. Replies
    1. This series is simply $\sum_{n=2} ^\infty 0$. Here we don't have to use any tests. Instead, we can appeal to the definition of an infinite series as the limit of the partial sums.

      $S_k=\sum _{n=2}^k 0 =0$

      Then $\sum_{n=2}^\infty 0 = \lim _{k\to \infty} S_k =0 $.

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  3. Replies
    1. I look at this problem and the first test that comes to mind is the divergence test.

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  4. Replies
    1. For this problem I used the root test (obviously) but I have a more general question. Are there any restrictions when multiplying top and bottom by the same term. Meaning can I always use (1/n) or (1/n^2), etc. or does the structure of the series restrict using any form of "1" that makes the problem easiest to solve?
      Does that make sense?

      -Erica

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    2. If it's a matter of determining the limit of a quotient of algebraic terms, you'll want to identify the greatest power of $n$.

      Consider the following expression:
      $$\frac{\sqrt{n^3+n}+n}{n+\sqrt{n}}$$

      I would identify the greatest power of $n$ to be $n^{3/2}$. Thus I would multiply and divide by $\frac{1}{n^{3/2}}$.

      Delete
  5. hi,
    just to make sure, do we need to graph polar coordinates for the test? What I understood in lecture today we don't need to right?

    Thank you
    Nahyr S. Lugo-Fagundo

    ReplyDelete
    Replies
    1. Hi Nahyr,

      Unfortunately, I wasn't in lecture today so I don't know. What were you told?

      Tim

      Delete
    2. That's what I understood, but I was just making sure if what I heard was right or wrong. If anyone from section could clarify this, that'll be great!

      Thanks!

      Nahyr

      Delete
    3. We won't be asked to draw graphs of polar coordinates for the exam, but they may be helpful to know to determine endpoints of integration, number of loops, etc.

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