Lesson on Monday 4th January: Students studying remotely, 1: please study this page; 2: print and complete the handout, 3: compare your solutions with solutions given, then 4: email me with any questions. Thanks, and see you soon!
Let’s examine . On this page, our values for are integers – a negative whole number, zero or a positive whole number.
We define the exponent to be a short hand notation for repeated multiplication.
On this page, we’ll look for the pattern made by integer exponents.
A summary of the laws can be found here.
The Product Law
Now we know that . Let’s write that in another way:
What we notice about the exponents is that they add up to four.
Let’s take a second example: suppose we have .
Writing that out in full give us:
This leads us to the law for the product of two powers with the same base: for any values , ,
Of course, the base doesn’t have to be 7; 7 is used here just for illustration.
The Quotient Law
Do you remember that a fraction is just a division? For example:
We also know that when a fraction has a common factor on numerator and denominator, it can be simplified. For example:
Usually, we don’t write out all of those steps. You might be more familiar with ‘scoring out’ or ‘cancelling’. Showing the steps without scoring out shows why scoring out works mathematically.
Let’s see how simplifying fractions helps with exponents. This time, let’s use ‘scoring out’.
Or, in otherwords, we see a common factor of on the numerator and the denominator. How many 7’s did we ‘score out’? We started with 5, we scored out 3, and we were left with 2. This leads us to the law for the quotient of two powers with the same base:
or, more generally,
The quotient law leads us to negative indices. Suppose we have .
Or, in general
When we say we mean, . When we say we mean one divided by three times over, that is:
which is really awkward notation and is not often used. Better to say:
Now suppose we have . Well, we already know that anything divided by itself is just 1.
Let’s see what happens when we apply the quotient law:
In general, (with the curious exception of a=0, but only sometimes…).
The Power Law
The power law tells us what do when we have a power of a power:
Distribution over a Product or Quotient
Now suppose we have the number , we know the answer is 100. Let’s write the number 10 as a product and then square it:
In other words,
This example illustrates that, in general:
Similarly, with division:
Take Care though – an exponent does not distribute over addition/subtraction!
The common mistake would be to say that is equal to but lets figure that out: which is not 49, so that is simply wrong.
Classroom handout Exponent Laws (typo table 2, 5^4 not 5^3)
Click to open the summary!
What might the value of be? What meaning does it have?
Using the product law, what is the value of ?
What about ? Does it have any meaning?
See if your calculator can make sense of and .