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 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.