New Zealand
Level 7 - NCEA Level 2

# Simplify and manipulate algebraic expressions

Lesson

We've already learnt that there are a number of conventions (rules) which need to be followed in order to solve problems with different operations correctly. This is known as the order of operations.

Remember!

The order goes:

Step 1: Do operations inside grouping symbols such as parentheses (...), brackets [...] and braces {...}.

Step 2: Do multiplication (including powers) and division (including roots) going from left to right.

Step 3: Do addition and subtraction going from left to right.

Each time we complete one of these steps, we simplify our equation until we get one final answer.

Let's look at an example so we can see this process in action.

#### Examples

##### Question 1

Simplify: $6x^2+4x^2\times5+7x^2$6x2+4x2×5+7x2

Think: Multiplication comes before addition. Then collect like terms.

 Do: $6x^2+4x^2\times5+7x^2$6x2+4x2×5+7x2 $=$= $6x^2+20x^2+7x^2$6x2+20x2+7x2 $=$= $33x^2$33x2

Many questions that you will encounter will often require expanding. As revision, we've summarised some methods of expansion in the table below.

Factorised form Expanded form
$A\left(B+C\right)$A(B+C) $AB+AC$AB+AC
$A\left(B+C+D\right)$A(B+C+D) $AB+AC+AD$AB+AC+AD
$\left(A+B\right)\left(C+D\right)$(A+B)(C+D) $AC+AD+BC+BD$AC+AD+BC+BD
$\left(A+B\right)^2$(A+B)2 $A^2+2AB+B^2$A2+2AB+B2
$\left(A-B\right)^2$(AB)2 $A^2-2AB+B^2$A22AB+B2
$\left(A+B\right)\left(A-B\right)$(A+B)(AB) $A^2-B^2$A2B2

Let's look at a few examples.

#### Examples

##### question 2

Expand and simplify: $\left(5x-9\right)\left(5x+9\right)$(5x9)(5x+9)

Think: This expression is of the form $\left(A-B\right)\left(A+B\right)$(AB)(A+B), so its expanded form will be a difference of two squares.

 Do: $\left(5x-9\right)\left(5x+9\right)$(5x−9)(5x+9) $=$= $\left(5x\right)^2-9^2$(5x)2−92 $=$= $25x^2-81$25x2−81
##### question 3

Expand and simplify: $\left(\frac{6y}{x}-\frac{3x}{y}\right)^2$(6yx3xy)2

Think: This expression is of the form $\left(A-B\right)^2$(AB)2, so its expanded form will look like $A^2-2AB+B^2$A22AB+B2.

 Do: $\left(\frac{6y}{x}-\frac{3x}{y}\right)^2$(6yx​−3xy​)2 $=$= $\left(\frac{6y}{x}\right)^2-2\frac{6y}{x}\frac{3x}{y}+\left(\frac{3x}{y}\right)^2$(6yx​)2−26yx​3xy​+(3xy​)2 $=$= $\frac{36y^2}{x^2}-36+\frac{9x^2}{y^2}$36y2x2​−36+9x2y2​

Try simplifying the following algebraic expressions below.

##### question 4

Expand and simplify:

$6\left(10x+8y\right)-6\left(-6y-6x\right)$6(10x+8y)6(6y6x)

##### question 5

Simplify $\frac{8x^2}{11}+\frac{5x^2-2x}{55}$8x211+5x22x55.

##### question 6

Simplify the following expression:

$\frac{x+3}{x+4}\div\frac{x+3}{3}-\frac{1}{x+4}$x+3x+4÷​x+331x+4

##### question 7

Expand and simplify: $\left(4st+\frac{2}{st}-4\right)\left(4st+\frac{2}{st}+4\right)$(4st+2st4)(4st+2st+4)

### Outcomes

#### M7-6

Manipulate rational, exponential, and logarithmic algebraic expressions

#### 91261

Apply algebraic methods in solving problems