1 Star2 Stars3 Stars4 Stars5 Stars 2.00 (1 votes)


This is in a textbook:

calculus caution

The area of a washer is pi*R^2-pi*r^2, which you can simplify to pi*(R^2-r^2), but not to pi*(R-r)^2. No matter how tempting it is to make the latter simplification, it’s wrong. Don’t do it.

1 thought on “Caution!”

  1. …this isn’t a fail…expanding pi*(R-r)^2 gives you pi*(R^2-2Rr+r^2)=piR^2-2piRr+pir^2, and not pi*R^2-pi*r^2…

Comments are closed.