Care to explain? I've never heard this one before.

Tarheel, you're right about L'H's rule. I was just giving the point in a very general sense.

Here's one for 1 = 0.

x = 1

dy/dx (x) = dy/dx (1)

1 = 0

Shameless, you just proved that the derivative of 1 is 0, which is perfectly legitimate.

Have you ever actually taken a calculus course?

It's a 'proof' for 1 = 0.

I could write a load of words if you don't understand:

let

x = 1

Differentiate both sides with respect to x and we get

dy/dx (x) = dy/dx (1)

or 1 = 0

I'm going to guess you thought that it should have been dy/dx = 0 but that would only be the case if I was using y = 1 and differentiating with respect to x.

Shameless, you're right, I interpreted what you were trying to do wrong. I thought you went from dy/dx (1) = 0 and proved that it meant 1 = 0.

Even still, your proof is invalid. "x" isn't a variable, it's the constant "x=1" as you set it up.

Now it just seems that you're just trying to test us, or you don't know what you're talking about. =P

Of course, it was just one of those false proofs like the one posted above. ;)

Trying to be tricky huh? =P I'll stop replying then, lets see if anyone else can answer your proofs.

 No 1 + 1 = 10

There's an easier way.  The slope of x = 1 is undefined.  Thus, you can't take the derivative of it.