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:
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
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