# Give Us Original Mistakes

Zeno might appreciate this (where “appreciate” is used in the technical sense of “bang head against wall on account of”). Via Isabel comes Eric Schechter’s page of Common Errors in College Math. If you survived calculus, read through it and congratulate yourself on all the mistakes you don’t make anymore!

(See how optimistic I am?)

Schechter provides one of the most inspiring examples of getting the right answer through the wrong method that I’ve ever seen. The problem is to evaluate the following definite integral:

$$\int_0^{2\pi} \cos x\, dx.$$

This is how our student started:

$$\int_0^{2\pi} \cos x\, dx = \left.\frac{\sin x}{x}\right|_0^{2\pi} = \frac{\sin 2\pi}{2\pi} – \frac{\sin 0}{0}.$$

But wait, there’s more!

$$\frac{\sin 2\pi}{2\pi} – \frac{\sin 0}{0} = \sin – \sin = 0.$$

And they say we can’t eliminate sin from the world.

## 4 thoughts on “Give Us Original Mistakes”

1. Ellipses fail me.

2. See, that’s just … an amazing demonstration in “memorization.” At least they got the answer right ;-)

3. The banging sound you hear is my head smacking up against the chalkboard.

4. manigen says:

I think I may have to get that framed and hung above my desk.