Algebraic expressions
Letters for numbers: like terms, values and writing expressions.
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A letter stands for a number. Only like terms can be added.
Look: 3x + 2y + 4x: the x’s join up to make 7x. The y’s stay apart: 7x + 2y.
✏️ Your turn!
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1Tidy up 6a + 2b − a + 3b
2Find 2p when p = 7
3Open the bracket: 3(x + 5)
! Careful!
✗3x + 2y = 5xy.
✓Different letters cannot join: 3x + 2y.
✗3x when x = 4 is 34.
✓3x means 3 × 4 = 12.
See the whole lesson on one page
A letter stands for a number. Only like terms can be added.
3x means 3 × x. Terms with the same letter are like terms: put them together. Numbers go together too.
Think of it like this3 apples + 5 apples = 8 apples. But 3 apples + 5 bananas stays 3 apples + 5 bananas. 3x + 5x = 8x, but 3x + 5y stays.
- Like terms
- Same letters: 4a and −a.
Solved together
Tidy up 5x + 3y − 2x + 7 − y. Then find its value when x = 4 and y = 2.
Group the x’s, the y’s and the numbers.
(5x − 2x) + (3y − y) + 7Put each group together.
3x + 2y + 7Now put in x = 4 and y = 2.
3 × 4 + 2 × 2 + 7 = 12 + 4 + 7 = 23
Answer3x + 2y + 7, which is 23.
Now practise it
Kanakku makes new questions on algebraic expressions every time. It shows the working and gives a hint when you are stuck.