Absolutely convergent series
I’ve seen many proofs that 1=2. Here’s a classic. The (not-so-subtle) error in the above proof is that we’re cancelling (a-b) on both sides, when (a-b) equals zero. That is, we’re dividing by zero on both sides. That completely invalidates the equality. Another proof uses the fact that the square root of a number can be both positive or negative. ...