1. Expressions, equations, formulae & identities Can you explain what these key words mean? Can you give an example for each one?

2. 2a + 3b + c is an expression is an equation is a formula is an identity

3. Expression An expression is made up of numbers and symbols, but expressions never have an equals symbol or inequality signs. Here’s some examples: 2a3x + 25y 2

4. 6a 2 + 7 is an expression is an equation is a formula is an identity

5. 2a + 3 = 21 is an expression is an equation is a formula is an identity

6. Equation An equation is made of two expressions that are linked by an equals sign Equations can be solved – this means you can find out what number the letter symbol stands for. Here’s some examples: 2a = 63x + 2 = 295y 2 =45

7. 2a 2 = 18 is an expression is an equation is a formula is an identity

8. 2a 2 + 18 is an expression is an equation is a formula is an identity

9. 2l + 2w = P is an expression is an equation is a formula is an identity

10. Formula A formula is a short way of writing some sort of rule, for example A = πr 2 is the formula for the area of a circle. A formula is a type of equation, but the symbols in a formula have set meanings, for example in the formula 2l + 2w = P l stands for length, w stands for width and P stands for perimeter.

11. is an expression is an equation is a formula is an identity

12. is an expression is an equation is a formula is an identity

13. is an expression is an equation is a formula is an identity

14. 2(a + 3) = 2a + 6 is an expression is an equation is a formula is an identity

15. Identity An identity is equation which is always true – this means it works no matter what number the letter stands for. There is a special symbol for an identity, this is sometimes used in place of the equals symbol. 2(a + 3) ≡ 2a + 6

16. 2a + 3b = a + 2b + a + b is an expression is an equation is a formula is an identity

17. F = ma is an expression is an equation is a formula is an identity

18. 2a + 3b = c is an expression is an equation is a formula is an identity

19. 5(x - 4) ≡ 5x - 20 is an expression is an equation is a formula is an identity

20. 5(x - 4) is an expression is an equation is a formula is an identity

21. 20(5 - x) = 100 - 20x is an expression is an equation is a formula is an identity

22. 5(x - 4) = 20 is an expression is an equation is a formula is an identity

23. Check up: Can you explain what these key words mean? Can you give an example for each one? expressionequation formulaidentity