Lesson 3. Subtract negative numbers

Subtraction as an Inverse Operation.

Subtraction is the same as the process of adding the additive inverse, or opposite, of a number to another number. The subtraction of numbers can be defined in terms of addition:

a – b = a + (–b) = c.

Thus, in order to subtract b from a it is necessary to add the negative of b to a. This means that addition and subtraction are inverse operations to each other.

Two signs together

8 – – 5 can be read as ‘8 take away negative 5’. This is sometimes written as 8 – (–5).

It is possible to replace two signs next to each other by one sign as follows:

EXAMPLES:

3 – –4

= 3 + 4

= 7

7 – 4

= 7 + (–4)

EXAMPLE:

The temperature is –5⁰C. It falls by 4⁰C. What is the new temperature?

Start at –5. Go down 4. Answer is –9.

So the new temperature is –9⁰C.

Lesson 3

•  Test 1 
•  Test 2
•  Test 3