How to express negative numbers in scientific notation?

I used -25 as an example:

= -2.5 × 101
(scientific notation)

= -2.5e1
(scientific e notation)

= -25 × 100
(engineering notation)
(one)

= -25
(real number)

Scientific notation is used to express very large or very small numbers. A number in scientific notation is written as the product of a number (integer or decimal) and a power of 10. The number has one digit to the left of the decimal point. The power of ten indicates how many places the decimal point was moved.