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Year 7AC9M7A02

Expanding Brackets

Formulate algebraic expressions using constants, variables, operations and brackets.

Expanding means removing the brackets by multiplying everything inside by what sits outside. Miss one term and the whole answer is wrong.

Builds onYr 7 · Like Terms and Collecting Them

Method

Multiply every term inside
3(x+4)=3x+123(x+4) = 3x + 12
The outside number reaches all the way across.
Take the sign with the number
2(x5)=2x+10-2(x-5) = -2x + 10
A minus outside changes both signs inside.
Expand first, then collect like terms
Do the two jobs in that order, never at once.

Worked example

e.g. Expand and simplify 3(x+4)+2(x1)\text{Expand and simplify } 3(x+4) + 2(x-1)
  1. Multiply the first bracket by 3.3×x=3x3×4=123 \times x = 3x \quad 3 \times 4 = 12
  2. Multiply the second bracket by 2.2×x=2x2×(1)=22 \times x = 2x \quad 2 \times (-1) = -2
  3. Write everything out with no brackets left.3x+12+2x23x + 12 + 2x - 2
  4. Collect the like terms.3x+2x=5x122=103x + 2x = 5x \quad 12 - 2 = 10
  5. Write the answer.5x+105x + 10

Practice

Expand every term, then collect.

1
4(y+3)4(y+3)
Answer4y+124y + 12
2
5(2a1)5(2a-1)
Answer10a510a - 5
3
3(x+2)-3(x+2)
Answer3x6-3x - 6
4
2(x+3)+4(x+1)2(x+3) + 4(x+1)
Answer6x+106x + 10
5
Why is 3(x+4)=3x+4 wrong?\text{Why is } 3(x+4) = 3x+4 \text{ wrong?}
AnswerThe 3 must multiply the 4 as well, giving 3x+12.\text{The 3 must multiply the 4 as well, giving } 3x+12.
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