what are some reasons we use negative numbers?

Answer 1

Negative numbers exist to provide solutions to equations of the form:

ax + b = 0

for positive constants a and b.

They also exist, more fundamentally, to provide additive inverses. For any number, take 5 for example, there is a number which we call "negative 5" or -5, where:

5 + (-5) = 0

For shorthand, we call it 5 - 5 = 0

In a "real world" way, the definition explains how subtraction is defined, in an abstract way. Without negative numbers, we would not have subtraction.

Answer 2

Negative numbers are very useful in vector analysis, which is absolutely essential for doing physics/engineering. The negative sign can be used to indicate the direction of a given vector: Usually, negative means that (at least one component of) the vector points south or west, whereas positive implies north or east.

Answer 3

stocks. We determine the value of the number that is either positive or negative.
Subtraction you have $5.00 you owe me $3.00, 5-3=2. You would have $2.00 lefto over for me anwsering your question.

Answer 4

Tempertures Below Zero
Overdrafts at banks
Debits from an account
Losses in business
When credits are less than debits