What do double negatives mean in mathematics

Why is minus minus plus: - (- a) = + a?

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We get a positive result when we make a negative number negative (or when we multiply two negative numbers together).

This results from logical approaches:

If we agree that a plus is a "yes" and a minus is a "no", then we see: 'So it has to be. We confirm the first yes with another, so to speak.

With minus minus, however, it is:. That is, we deny a no, which becomes a. The negation or inversion of is.

We can look at this fact too Negation questions notice:

"Didn't you like the movie?" (A no question). If we now answer "No", we logically deny this statement "I didn't like the film." To: "I liked the film Not I didn't like it. ”→ As a result, I liked the film.

Even if it seems a little complicated, make a short and concise note: as fixed or defined.

Minus times minus equals plus (approach 1)

A descriptive derivation of the rule of can be given via the distributive law:

Use example values

Now the question arises, what value must assume in order for it to ultimately result in? Right, a positive one.

Minus times minus equals plus (approach 2)

Another, somewhat longer way is the following, but for this you need to understand how to rearrange equations:

As we can see, at the beginning and at the end, both have the same value and are therefore positive.

Minus times minus equals plus (approach 3)

When it comes to division, every number results from itself, so:

This also applies to negative numbers, for example

And right, the result is positive, so .

Negative value through negative value results in positive value.

Here one could conclude (since the division is the reverse of the multiplication) that minus times minus must then also result in plus.