Author: mpershan

Finding f(x) from f'(x)

There’s a lot to think about in this problem. But where is this student having trouble, and what would you do with the student next?

Problems with Proofs

The proof above isn’t great. In the comments, take on any of the following questions (or any others):

Sometimes kids slap stuff together when they’re confused, and other times they’re substantively mistaken. Which is this, and what evidence supports your position?
How would you help this student recognize that the logic in his proof doesn’t flow?
What would your next steps be in working with this student? What sorts of problems would you ask him/her to solve?
From the picture above, what evidence of knowledge do we have?

Tags G-CO.10

5.NBT.3 Decimals

From Khan Academy: Comparing Decimals

Post author By mpershan
Post date July 17, 2012
6 Comments on From Khan Academy: Comparing Decimals

No, Sal Khan did not actually submit this question. But Andyhav3 asks:

What’s this student getting at with “the right side of the decimal,” and how might you help Andyhav3?

[Click here to see how your approach compares to how his question was actually handled.]

Tags 5.NBT.3

Limits

“The limit does (not) exist”

Post author By mpershan
Post date July 17, 2012
5 Comments on “The limit does (not) exist”

Sorry for the title of this post, but I really wanted to link to this video.

Anyway, what’s going through this students head? What would you say to the student when going over the problem?

(Also, remember to drop into the comments of this post and leave some feedback about the site.)

Site Business

Open thread for feedback

It’s the Math Mistakes 3 week (or so) anniversary!

I’m opening this thread for feedback on the site. In the comments, tell us what you like. More importantly, tell us what you don’t like so that we can get better.

Here are some things that I’d like to hear about:

The look of the new site
The quality of the mistakes that are posted
The experience of analyzing the mistakes — do you find it challenging, or is it easy to understand and respond to a student error?
The quality of the prompting questions in the posts
The ability to browse mistakes using the menu on the left

I’ll end the post with a quick plug to send us your or your students’ mistakes. If you find yourself going back to school, remember to bring a camera and find 4-5 interesting errors to send in. Especially if you teach K-8 or college math.

logarithms

Dividing by “log”

Last week we posted a somewhat similar mistake involving logarithms. Here’s the student work:

While you should feel free to comment on today’s mistake independent of the earlier one, I think it would be especially productive to compare these two pieces of student work. Could the same student have done both pieces of work? Are there differences between the way each student understands logarithms?

By the way, we now support equation editing in LaTeX, so feel free to write things such as $\frac{2\log(6x)}{\log}$ in the comments. This post is also tagged with a Common Core Standard and categorized according the hierarchy that you see in the menu on the left.

Tags F-BF.5

Radicals Radicals

Algebra 1 factoring horizontal and vertical lines linear functions

“Graph x = 3”

The mistake is pretty easy. But what’s the underlying misconception?