Expressions, equations, formulae & identities

Can you explain what these key words mean?Can you give an example for each one?

2a + 3b + c

is an expression

is an equation

is a formula

is an identity

Expression

An expression is made up of numbers and symbols,

but expressions never have an equals symbol or inequality signs.

Here’s some examples:2a 3x + 2 5y2

6a2 + 7

is an expression

is an equation

is a formula

is an identity

2a + 3 = 21

is an expression

is an equation

is a formula

is an identity

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 = 6 3x + 2 = 29 5y2=45

2a2 = 18

is an expression

is an equation

is a formula

is an identity

2a2 + 18

is an expression

is an equation

is a formula

is an identity

2l + 2w = P

is an expression

is an equation

is a formula

is an identity

Formula

A formula is a short way of writing some sort of rule, for example A=πr2 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.

𝑎2+𝑏2=𝑐2

is an expression

is an equation

is a formula

is an identity

𝑎2+𝑏2

is an expression

is an equation

is a formula

is an identity

𝑎2+42=52

is an expression

is an equation

is a formula

is an identity

2(a + 3) = 2a + 6

is an expression

is an equation

is a formula

is an identity

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

2a + 3b = a + 2b + a + b

is an expression

is an equation

is a formula

is an identity

F = ma

is an expression

is an equation

is a formula

is an identity

2a + 3b = c

is an expression

is an equation

is a formula

is an identity

5(x - 4) ≡ 5x - 20

is an expression

is an equation

is a formula

is an identity

5(x - 4)

is an expression

is an equation

is a formula

is an identity

20(5 - x) = 100 - 20x

is an expression

is an equation

is a formula

is an identity

5(x - 4) = 20

is an expression

is an equation

is a formula

is an identity

Check up:

Can you explain what these key words mean?Can you give an example for each one?

expression equation

formula identity