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Grade 9

Multiply and divide algebraic terms with indices


We've already looked at how to simplify and substitute values into algebraic expressions. Now we are going to look at how to add subtract, multiply and divide algebraic fractions. The processes we follow with algebraic fractions are very similar to the processes we use with fractions that only contain numbers. Let's check it out.

Adding and subtracting algebraic fractions

Do you remember that when we are adding or subtracting fractions, we need to have common denominators? Well, the same goes for algebraic fractions. We need to find a common factor between the fractions (remember you can always multiply the denominators together to find a common factor).

The process

1. Find a common denominator

2. Multiply the numerators by the same number as the denominators to keep the fractions equivalent

3. Add the numerators

4. Simplify the fraction if possible.


Multiplying and Dividing algebraic fractions

We've already looked at how to multiply and divide fractions, and the processes are the same for algebraic fractions. We just need to consider any algebraic factors when we are simplifying our answers.


More examples

Question 1

Simplify $\frac{8x}{12}+\frac{10x}{12}$8x12+10x12

Question 2

Simplify the following: $\frac{-2x}{11}\div\frac{7y}{5}$2x11÷​7y5

Question 3

Simplify the following: $\frac{-3x}{7}\times\frac{12y}{7}$3x7×12y7


We've already seen about exponent laws already. Now we are going to look at how to apply these rules in questions with algebraic expressions. A power indicates how many times a number is multiplied by itself. For example, $m^3=m\times m\times m$m3=m×m×m. Let's look at how we can build on this knowledge.


Exponent Rules With Algebraic Expressions

Product rule

The product rule states: $a^m\times a^n=a^{m+n}$am×an=am+n

Let's look at how we derive this rule using an example. Say I wanted to simplify the expression $a^5\times a^3$a5×a3. In an expanded form, this would mean $a$a multiplied by itself 5 times multiplied by $a$a times itself 3 times:

So, you can see that $a$a is now multiplied by itself 8 times, which we can write as $a^8$a8 (which is the same as adding the powers, i.e., $a^{5+3}$a5+3).


Quotient Rule

The quotient rule states:$a^m\div a^n=a^{m-n}$am÷​an=amn

This is derived in a similar way to the product rule. Say we wanted to simplify the expression $a^6\div a^2$a6÷​a2. In expanded form, we would write this as:

You can see I've taken out common factors to simplify the expression, leaving with an answer of $a^4$a4 (which is the same as subtracting the exponents, i.e., $a^{6-2}$a62)


Let's Simplify

Now let's look at how we would use these rules to simplify an algebraic expression.


Simplify: $\frac{4h^3}{16h^5}$4h316h5

Think: If we wrote this in expanded form and simplified the fraction by taking out common factors, it would be:

So, if we were writing our simplified answer with a positive exponent, our answer would be $\frac{1}{4h^2}$14h2. We could also write this with a negative exponent as $\frac{1}{4}h^{-2}$14h2.


More examples

Question 4

Simplify the following expression, giving your answer with positive powers of $u$u:


Question 5

Simplify the following, giving your answer in exponential form: $\left(-5n^3\right)\times m^4\times\left(-5n^3\right)\times m^5$(5n3)×m4×(5n3)×m5.

Question 6

Convert to fraction form and simplify:

$\left(\left(-4v^8\right)\times u^4\right)\div\left(\left(-2v^8\right)\times u^{10}\right)$((4v8)×u4)÷​((2v8)×u10)





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