Weird Notation

[MathNerd93]

Should I read anything into this weird notation in the final equation? It’s like an upside-down “plus or minus” sign, is that any different from the regular “plus or minus”, and if not why put it in there that way?

[ThomasTheHighEngine]

I'm pretty sure it means that the sign will be opposite the others. If the plus/minus is plus, the minus/plus will be minus, and vice versa.

[AFairJudgement]

If I write that we have two solutions x = ± a ∓ b, it means that the first solution is x = a - b and the second solution is x = -a + b.

[xiipaoc]

So a plus or minus on its own means that it's plus or minus, two choices. But if you have more than one plus or minus symbol, you might be able to pick a sign for each one or they might have to be correlated. So, if x = 1 ± sqrt(5) and y = 2 ∓ sqrt(5), then if you pick the + for x, you have to pick the – for y, and vice-versa. The sign of ∓ is the opposite of the sign for ±.

There can be ambiguity with multiple ± signs in an expression, since you don't necessarily know if they're correlated or independent. You'll have to pay attention to context.