What does a * B mean in mathematics

What does a * B mean in mathematics

*A * B means a times B

There is a problem of quantifier and full quantifier
∀ X & # 8707; y, x + y = 0 is true
∃ Y & # 8704; X, x + y = 0 is false
Domain is Z

First of all, we need to make clear the order. The first is to say that there is a Y for any X
It's a one-to-one relationship: if there's an X, there's a y. in fact, the y you find is - X
The second is that there is a one to many relationship between Y and any x, that is to say, for a Y0, it and all x satisfy Y0 + x = 0, which is obviously impossible

What's the meaning of a written upside down in the mathematical symbol?

The inverted "a" - the initial of any means "arbitrary"

What's the meaning of "△" in mathematics? What does it stand for?

1. Triangle s △ =
2. Variable △ t = t2-t1
3. The discriminant formula of equation root number △ = B ^ 2-4ac