My Question

I believe this question is quite easy but lets not neglect these simple questions.

Investigate lim(x->0) (1-Cos(h))/h^2 numerically and graphically. Then prove that the limit is equal to 1/2.

Posted in Test #1 Review | 1 Comment

test review

1) let f(x)= \frac{1}{x^2+1} and g(x)= x^2+5x-1

differentiate:

f(x)+g(x), f(x)*g(x), f(x)/g(x),( f(x))^g(x) and \sqrt{g(x)}

2) f(x)= \frac{x+2}{1-|x|}

a) evalute the continuity at x=0

b) Is the function derivable at x=0?

Posted in Test #1 Review | 1 Comment

My Question(s)

Fairly easily. I can surely say we can all agree we don’t want any hard questions. (PS: I have no idea how to use laTeX, so I hope you guys can understand my fail attempt to write a math problem online.)

1) The limit below represents the derivative of f ‘(a). Find the f(x) and the a values.

Lim h->0 of ((3+h)^3) – 27)/h

f(x) = ?

a = ?

2) Find the slope of the secant line through the points of x = 2 and x=4 of the function f(x) = x^2. ( Not sure if I typed this correctly I was half asleep when I woke up: Correct me If I’m wrong)

Slope= ?

 

Posted in Test #1 Review | 4 Comments

Test Review Question

In y=mx+b form, what is the equation of a line tangent to f'(x) at x=1/2 if f(x)=e^(2x)+3x-6?

Posted in Test #1 Review | Leave a comment

Test # 1 Peer Review Question

Peer Review Test 1

Sorry for the picture. Will need time to get used to latex.

Posted in Test #1 Review | 1 Comment

Peer Review Question

Sample peer review Q for the test.

Is the derivative of a product the same as product of the derivatives?

i.e. it is true that

\frac{d}{dx}\left(f\left(x\right)g\left(x\right)\right)=f'\left(x\right)g'\left(x\right)?

Find a counterexample:

(aka Prove the product rule).

-Izzy

Posted in Test #1 Review | 1 Comment

Homework #5 – comments

Homework #5 grades are now posted in Blackboard’s grade center. Don’t freak out that the grades are low:

  • There were only three questions and I think one in particular was a little hard
  • The grade you see is out of 15, not 25 as usual.

While it’s fresh in my mind, I think it’s worth commenting on your work. For the most part, the work was good, but Section 3.3 #64 was a minor disaster. (Again, don’t worry, I knew that’d be a harder one for you so I’d have been surprised if everyone got it.)

Please see my own hand-written solutions: Solutions5

I didn’t assign these questions because I care all that much about multiple roots, I just wanted you to be able to think about the kinds of arguments you can construct using derivatives and, in this case, the product rule. So you really had to think about two things while answering this question:

  1. Calculus
  2. Logic

What I mean by #2 is how to construct an argument to prove something. It’s hard to think about both things at once and I’d like to focus here on #2.

In math, when you are proving Statement A is true if and only if Statement B is true, you’re really proving two things.

  • Assume Statement A is true. Use this to show that Statement B is true whenever Statement A is true. For shorthand, I’d say A implies B or if A then B. In this case, I’d say Statement A is: f(x) has a multiple root at x=c and Statement B is: f'(x) has a root at x=c.
  • Assume Statement B is true. Use this to show that Statement A is true whenever Statement B is true. Here, you’re showing B implies A, or if B then A.

If you haven’t worked with it before, the if and only if part of the question might throw you off. It can be particularly hard to keep track of what you’re assuming and what you’re proving. I think one reason for that is that by proving A implies B and B implies A, you’re actually saying that Statement A and Statement B are equivalent. When two things are equivalent, well, it’s hard to tell them apart! So you might accidentally assume the thing you’re trying to prove.

Compare the A if and only if B kind of result to the simpler kind A implies B. We saw an example of a result like this in class on Monday: Statement A is: f(x) is differentiable at x=c and Statement B is: f(x) is continuous at x=c. We proved that if f(x) is differentiable at x=c, then f(x) is continuous at $x=c$. We also saw a counterexample to the statement B implies A. Having just one counterexample proves that B implies A is false. Our counterexample was f(x)=|x|, which is continuous, but not differentiable at x=0. I probably said something like, “Differentiability is strictly stronger than continuity,” or, “the converse does not hold.” What I meant was if f(x) is differentiable at x=c, then f(x) is continuous at x=c BUT if f(x) is continuous at x=c, then f(x) may not be differentiable at x=c. So A implies B but B does not imply A. Therefore, A and B are not equivalent in this case.

It can also be hard to tell the difference between a proof and an assumption, or even a reason for saying something is true. I can comment more on that later, but if this kind of stuff interests you, you might like to take a class in logic.

Posted in Homework | 2 Comments

1. If f'(x)=x^3-12x+2, at what values of x would f ‘(x) have roots?

Posted in Test #1 Review | 4 Comments

Written homework solutions 2, 3, 4, 5

Here are my own solutions for most of the written homework that you’ve submitted so far. Let me know if you have any questions.

Solutions2

Solutions3

Solutions4

Solutions5

Posted in Homework | 1 Comment

Test #1 – March 12

Test #1 will be given in class next Wednesday, March 12. It will cover everything up to and including this Wednesday’s lecture. This includes Chapter 2 except for 2.8 (there’ll be an extra-credit question like those in 2.9 but otherwise you’re not responsible for 2.9) and Chapter 3 except for 3.4, 3.5, 3.10, and 3.11 (we’ll cover those sections after the test). Don’t forget to contribute to the class’s review sheet here.

Posted in Uncategorized | Leave a comment